If you're going to groundschool, you wont have a test the moment you walk in the door. The first day is usually just indoc to the company and how things work, fill out the usual forms, put out a fire and such.

Once you arrive in the CLT training facility you'll go over the FOM for a few days and then have a test on it. Then its limitations followed several days later by systems. This will all be explained to you on your first day at groundschool. You will have enough time to study for all of the tests and still go out for a bite to eat. My experience was that some people had to study more than others, if you know what study techniques work best for you personally then stick with that and you'll be alright. Expect to study more than you would for finals in high school or college, but don't expect to pull any all-nighters.