It always has been 6 months, but there is the option for the UFC to grant excemption in "special situations" like they did with Brock Lesnar, UFC will do what they have to do, if he signs for a fight they wont keep him from fighting for 6 months.
What i dont know 100% and this isnt related directly to Conor is if a fighter has to be 6 months on the pool to then be able to sign for a fight months after, or they can sign the fight lets say, 6 months in advance, and then fight the day after the 6 months deadline is met, which is it??