I made my own timeline for the film and its similar to the one I'm going to post for you. I don't usually post things like this in full but in this case I think its important and I think its the most accurate one I have ever seen. I would highly recommend if you want to understand the timeline you read it, it gets very interesting.
Starting here.
We have eight characters, who are four couples: Emily-Kevin, Amir-Laurie, Mike-Lee, Hugh-Beth. Let's suffix 1 to all of the original people in the first house, which we will call House 1. Kevin and Laurie had dated previously.
So we know what happens in the dark zone: every time people pass through it, they end up in an alternate reality house that isn't the house they originally left. There are also two boxes: one that comes into the house and one that they make in the house. The boxes have random objects, which are primary identifiers.
Emily1 is the primary character from the first scene of the movie, so we'll keep her as constant and explore the movie.
Emily1's phone screen cracks. She then heads to dinner in Mike and Lee's house, House1. Soon after, Hugh's phone screen cracks too.
They recount life stories at dinner and Kevin tells one about his time with Laurie, causing Emily to be upset with him. Emily then talks about previous comets in Finland and Siberia that caused inexplicable phenomena, such as flattening of trees and a crazy lady who claimed the man in her house wasn't her husband because she had killed her husband the previous night.
Suddenly, the power goes out. Mike1 comes out with three sealed boxes of glowsticks -- red, blue, green. House1 breaks open blue glowsticks.
House1-Blue-Amir1, Emily1, Kevin1, Laurie1, Beth1, Lee1, Hugh1, Mike1.
Amir1 and Hugh1 go out exploring. Some other Hugh (as we now know) knocks violently on the side door but disappears. None of the group is aware of this, but Amir1 and Hugh1 come back soon with the first box. Box1 contains a ping pong paddle as the random object. (We don't really need to remember the die numbers for each individual).
Each of their photos has a number on the back that Emily notes down on a notepad in red ink. There is no number 3.
So
House1-Blue glowsticks-PingPongPaddle received.
Lee1 gives Hugh1 a cloth band-aid for his forehead. They discover the duplicate note on the door and Hugh1 reveals that he saw the same group in the other house.
Now, Emily1, Kevin1, Mike1, Laurie1 go out exploring with the blue glowsticks...
and run into their alternate selves with the red glowsticks.
They pass through the dark zone and come back into what they think is House1 but is actually, let's say, House2.
Lee and Beth have never left the house, so House2 contains Lee2, Beth2, Emily1, Kevin1, Laurie1, and Mike1. We think it's still Amir1 and Hugh1, but when the second group talks about how they had the blue glowsticks and the other people had the red one, Hugh and Amir realize they're in the wrong house.
They see the boxes:
.. have a discussion,
.. and [upon second viewing], we now know that these are Hugh and Amir who do not have blue glowsticks. But House2 still has blue glowsticks, so these are Amir3 and Hugh3. Everyone confirms as having passed through a "dark zone that was darker than the rest of the area".
So, we have,
House2-Blue glowsticks-Received object unknown-Lee2, Beth2, Amir3, Hugh3, Emily1, Kevin1, Mike1, Laurie1.
Beth2 now tells Hugh about the book in his car that he and Kevin retrieve. They don't leave the premises, so we can assume they're the same selves that went out of the house. Lee2 is napping. The group find out about the Multiverse theory, Schrodinger's cat, yada yada. An argument breaks out about whether the group has reacted with the other group (remember, they still think there are only two groups), and Mike1 thinks killing the other group is a good idea because if the other Mike is drinking, he could come kill this group.
Mike1 then recounts that in the other house, he saw Amir, Hugh, and Lee, but not Beth. But in this house, Lee is taking a nap. So they figure that in the house from the other reality, Beth is taking a nap, and not Lee. Since Beth was the one who put the book in the car and remembered it, they think the other house doesn't have the book. Mike thinks it would be a good idea to prevent the house from the other reality from getting the book and preventing them from having the conversation, but everyone disagrees with his idea of going and getting the other book from the other car. Mike1 then tells Kevin1 that he's going to leave and put the note about Beth to blackmail his own self to prevent the other Mike from getting the book. Mike1 now leaves the house.
The group now finds out that Beth had given Lee the drops. Emily1 and the group wonder about the drug in the food. After the discussion in the kitchen with the drops, Lee asks Beth about her vase.
... a conversation that Emily realizes the two characters already had much before the dinner party started (in House1):
Hugh and Amir sneak off with their red glowsticks:
and make plans to take the book and the box and leave, while Mike returns (after leaving the self-blackmail note in the other house)
When asked where he went, Mike goes and gets a drink. We now know that despite his blue glowstick, he isn't Mike1. Let's call him Mike4 because we do not know where he came from. (He can't be Mike3 because Hugh3 and Amir3 have red sticks. He could be Mike2, though.)Mike4 tells Kevin1 how he dropped the letter off, was going to smash the car window and take the book out, but didn't. (Note that at every point any character runs into a choice, there is a difference created in the alternate reality). Mike says he's been out 45 mins while Kevin tells him he was barely out for five mins.
Meanwhile, Hugh3 and Amir3 wrap up the box they brought and put back their oven mitt random object in and leave.
So we have
House2-Blue glowsticks-OvenMitt Received- Lee2, Beth2, Mike4, Emily1, Kevin1, Laurie1.
Mike starts drinking and the others realize that Hugh and Amir are missing, along with the box and the book. The group realizes that Hugh and Amir have been acting strange and could have been alternate Hugh and Amir. Beth then points out that everyone except herself and Lee have left the house at some point. Laurie kisses her ex, Kevin, and Beth tries to tell Emily after seeing it. Lee2 confronts a semi-drunk Mike4, and Emily1 confronts Kevin1. The lights go out again and they hear a crash.
Everyone goes out to investigate with their blue glowsticks and see that the car's glass has been broken. They don't realize that this was probably another Mike making a different choice. Everyone goes to make sure their respective cars are alright, and Emily1 retrieves her ring that Kevin gave her from her car and hugs Kevin. When she asks the caring Kevin if everything is okay with Hugh's car and Kevin is confused, they realize that they are both from different realities. Emily1 goes back into House2 and finds Kevin1 there, indifferent. The group try to figure out why
they would break into Hugh's car, when Hugh and Amir return with the book.
The new Hugh and Amir recount their story, starting from when they first left the house to make a phone call the very first time. Hugh talks about how he saw the same dinner table and hit his head when everyone interrupts them to tell them they already came back and left. Lee then realizes that she had given Hugh a cloth bandaid instead of the one he was wearing. They say that they were in a house where everyone had red glowsticks that they produce, and they confirm that the red glowsticks here are still unopened. The group then realizes that these two are the original ones who left. They also have the blue glowsticks.
But they passed through the dark zone. So let's call them Hugh5 and Amir5 (to differentiate from Mike4). When they talk about the notes, Hugh5 says the other house ended up with two notes, while this house has two notes as well, which would mean the notes were written at least 4 times. They now realize there are more than just two realities.
To keep themselves sane and mark their own house, they realize they need a unique identity that's random and can't be repeated. Since it's an alternate reality, they realize the pictures are from this house. They get a die and decide to allot a number to each person, and then realizes they are doing the same thing the other house did ahead of them -- they were creating their outgoing box.
Emily writes down the numbers with a blue pen since it's a "blue house". They include a coaster as the random object in the outgoing box.
As they roll the die each and Emily notes the numbers down behind every individual's picture. When she checks the earlier notepad where she noted down the numbers from the received box, she realizes that the numbers as well as the color of the pen are different. There are occurrences of '3' which were absent in the box House1 got.
Emily1 now realizes that she's in a different house. She then notices that Hugh uses his phone and the screen isn't cracked.
Emily1 now tries to make everyone remember their previous incoming numbers and compares them with the numbers she remembers from the box House1 received.
Beth confirms she got a 3, Lee confirms she got a 5 (since they both never left the house). Kevin says 6, Emily remembers herself as having a 4, and Hugh says his number was 3. (In the House2 list, Emily and Beth are 3). Emily now realizes that Hugh is from a different reality as well. Emily shows the numbers to Mike and explains to him that they are visitors and that this Lee isn't his wife.
She also tells him that since Hugh's phone wasn't cracked, he's from a different house. She explains her hypothesis that the dark zone is like a roulette wheel that takes everyone to a different destination. She states that they should go back to the dark zone to find their reality before the comet passes or else they would be stuck in this one.
Suddenly, Mike's self-blackmailing letter saying "Beth + book = Trinidad club don't let it happen buddy" slides under the door. The note is read by Hugh, who then discovers that everyone knew about Mike and Beth getting together 12 years ago, except for him, despite the fact that everyone thinks he already knew. They start to argue when Mike and Emily ask Hugh to produce his phone. When the rest of the group sees that the screen isn't cracked, they get a shock. They then try to recall the first box's random item. Hugh's and Amir's was a stapler, Lee and Beth's was an oven mitt, Emily, Kevin, and Laurie had a ping pong paddle, while Mike's was a napkin (so he isn't Mike2).
House2 - blue glowstick - oven mitt received - Lee2, Beth2, Mike4, Hugh5, Amir5, Kevin1, Emily1, Laurie1.
Hugh and Mike have a fight after a drunken Mike provokes an enraged Hugh even further. While everyone drags Hugh away, Mike wonders aloud to Emily if they are the darker versions of themselves. Suddenly, yet another Mike with a green glowstick bursts in, beats up this Mike, and leaves.
The group realize that Mike4 is probably dead (just like Mike1 wanted to kill). Beth's nose starts bleeding and Laurie acts possessed. Kevin goes to calm her down. Emily opens the door and finds yet another note on the door. She then leaves, disillusioned with the group.
She passes by houses that have a stuffed monkey as a random object, inside which she sees a sad version of herself, another where she sees Hugh and Mike in a shouting match, and one where she sees Kevin and Laurie happy together. She sees the comet passing and then chances upon a house that is still well lit, where the entire group is happy and chatting, where her alternate appears happy with Kevin. She enters the house stealthily, grabs a baseball bat, and removes the hallucinatory drug from the kitchen.
Let's call this House9. House9 suddenly hears a crash outside. They decide to go investigate and jokingly talk about getting glow sticks. (We realize they never took the glow sticks out at all and have just been sitting inside their house and chatting the entire time.) They notice outside that Hugh9's car's windshield is cracked. Everyone decides to check if their own cars are alright, and Emily9 goes to grab her ring from her car.
As she is wearing the ring, Emily1 punches her and puts her in the car's trunk. Emily1 then comes back into House9, where everyone is happy and affectionate. It appears that Emily1's career mistakes have not been made by Emily9, who has the seemingly perfect life made out of good choices. While they go out to see the comet pass, the lights go out and come back. Emily1 suddenly sees Emily9 crawl back into the house. She then proceeds to hit her on the head with the toilet tank's lid and hides her in the tub.
Before she's about to leave the bathroom, Emily1 suddenly realizes her ring's missing, and takes Emily9's ring off and wears it on her finger. As she leaves the bathroom, we see that her ring is lying on the floor. She goes out and collapses.
Emily wakes up on a bright and sunny day, still in Mike and Lee's house. She goes towards the bathroom to investigate when Beth comes out of the shower. Outside the house, she sees that Hugh's car's windshield is still broken and upon looking in, she finds the book still in the car. Kevin comes by and tells her she passed out and hands her her ring, saying he found it in the bathroom. Emily notices she's already wearing her ring, and now has two.
Kevin suddenly gets a phone call from Emily's number and answers it, and slowly turns towards Emily.
Emily then realizes that the previous night was no dream.
The movie ends with Emily1 realizing that she's in the same reality as Emily9.
https://www.quora.com/Can-someone-make-a-coherent-and-chronological-timeline-of-the-film-Coherence
So yea, that is a lot to digest but appears to match closely with the film if not exactly.