All I know is he was told and taught 27 days for habitual behavior. Surely if you went to school you have heard of how long it takes to break a habit. That is not to say that some alcoholics or other addicts don't relapse but its a mental problem.
His school was/is behind the curve. Which is not surprising as addiction awareness and understanding are lacking--but getting better all the time.
There is no such thing as breaking an addiction. Addiction is a progressive mental illness. It is either active or in remission. It never goes away, but it is manageable via treatment and ongoing life-long maintenance. It is a chronic, medical disease a la diabetes--as defined by the AMA and every other scientific body/organization in the developed world.
The 28-Day time period is a result of whatever actuarial math was/is used by the insurance companies. Drug/alcohol treatment coverage used to be open-ended, but the success rate for long-term, meaningful recovery is statistically dismal. Short of open-ended, addiction experts consider three months an ideal amount of coverage--depending the individual's stage in the progression.
A more "appropriate" question for the people who are suspicious of the legitimacy of JBJ's entering treatment is whether or not he is an addict at all. With the DUI and what seems to be a considerable body of rumor about coke-use the chances are high that he is. But the lofty height at which he functions professionally and the fact that he has passed random tests since 12/4 suggest he could be in early stages. Or, technically, not an addict.
We will "know" a lot about the extent of JBJ's problem when he is discharged from treatment and reenters the public eye. If he's out three weeks from now and picks up training/fighting along a natural timeline we can be somewhat sure that he has arrested early stage addiction. (Obviously, this set of circumstances throws fuel on the doubters' fire.)
If he stays remains in treatment longer than the 28 days, or transfers elsewhere and limits his public exposure to a request for privacy, it will be reasonable to guess that he suffers from advanced stage addiction. In which case he will likely be gone for anywhere from 3 additional months to more than a year.
Frame of reference: Tiger Woods dealt with sex addiction issues and was away from golf for 9 months.
If I'm trying to read it like a poker hand, I put him on a return to training early next summer with a fight in September. Give or take 60 days, I'd give that a 30% chance of accuracy.
*As people consider and judge the situation they should try to avoid applying a personal standard. The VAST, VAST majority of people who use drugs/booze are not and never will become addicts. Even the people who you would consider "heavy users" are more likely to avoid addiction than to contract it.