RDAP and testifying (snitching) are the only two ways to cut time off of your sentence in federal. If you are eligible, you should definitely transfer to a women's camp that does have RDAP because it is worth it. I took it and got a full year off of my sentence. 

There are some institutions that reward trustees with some extra good time, but that isn't necessarily the norm. We cannot name one that does but have heard there are some, somewhere.

Good time is granted at the beginning of the sentence and can only get lessened if the inmate gets into trouble and has it taken away. If you are a federal inmate, there is a program that can take one year off their sentence if they qualify. It is called RDAP - the inmate would need to have a pre-existing drug or alcohol issue prior to incarceration.

Yes, the 85% is in effect and there isn't anything you can do to change that. There are some programs in other states that might shave off a few months, but we are not privy to any for the Mississippi Department of Corrections.

180 days is hardly a sentence. 

All inmates receive "good time credits" when they begin their sentence. Usually, that is 15% and that is the most it can be, it can only lessen by bad behavior. The one way for early release is if the inmate has information about another crime or criminal enterprise that would lead to the prosecution and conviction of another. THAT is also called snitching (not recommended) and it could carry repercussions on the yard, but the weak-minded always look for a short cut.

Inmates are credited for time that is spend in custody, whether it is for an hour in another county, that counts as "one day served". Therefore, the 90 days spent somewhere will definitely count towards his release date calculation

If he has a release date, that is the outdate - unless he does something untoward that causes him to get jacked-up for more time. Once the release date is posted, it would include any good time accrued.

The judge has nothing to do with the allocation of good time. The good time credits are set by the State's Justice Department. If the program you speak of offers a sentence reduction for successful completion, tit doesnt matter what the judge wants, they hold zero power over the Department of Corrections as they follow their internal procedures. I know this sounds harsh, but a 16-month sentence is a joke compared to the time we've all done - he'll be fine

Unfortunately, there are no programs for early release for sex offender in the state of Maine. There are mandatory programs that the inmate must complete but none leads to a shortening of the sentence. Then there is the long probation period following release along with mandatory registration in the Sex Offender Registry that remains on their record forever. Here is a link to the ME DOC pdf that explains their program.