It's the Phase system now. For my AIT (at Fort Meade, MD), we spent the first 4 weeks at phase IV. In this phase, we couldn't wear civilian clothes or leave post. And we couldn't leave the company area without a buddy. We were also required to be in our rooms for bed check at midnight on the weekends, but then we could get up and go to the day room.
After that was phase V, which we were at for 5 weeks (I think). As a Phase V, we had civilian clothes and could leave post on the weekends. Bed check was at 2 a.m. unless you were signed out for the night. As a phase V we were allowed to stay one night off post on the weekend, but it's not like that anymore.
After that, if you were still there, you phased up to VA. At VA, you could leave post any day of the week, but on school nights you had to be back for 9 p.m. bed check. You could also spend both Friday and Saturday nights off post, this has since changed to only one night a weekend off post. If you aren't signed out to be somewhere, bed check is at 2 a.m.
Also, we weren't allowed to drink until VA.
Anyway, that's how it was where I was. It's different everywhere, though.