I took my class on Thursday mornings and was given the entire day off now I think it really just depends on your work location though. Mine just chose to give me the entire day off for my class.
Getting time off really depends on where you work. I originally signed up for a class and ended up being scheduled off that entire day every time (I dropped the class though because I'd rather not have my day off taken up by a class). Other people in the same class I was in had to go to work directly from class.
You are given days off every week though (most of the time it's two days off unless it's a busy time). Disney isn't concerned about classes you are taking from actual colleges or universities though. You must realize that first and foremost you are there to work for Disney, not take classes.
If you want the same days off every week than you can request them though the HUB (Online Disney database thing where you view your schedule and pay stub and all that). I ended up requesting the same days off every week so I would get days off with the people I was friends with because if I didn't my days off never coincided with theirs.
Unless you do this you can't be sure of when you'll have off every week...