The cadets only need to be in their rooms appearing to study...depending on when you actually go, you may or may not be with a cadet who has work to do. Most visitors bring their own work from home or else a good book. If you are there during the week, (for example a Tuesday, which is club night) you will accompany your host to his/her club. If it's a weekend, you'll do whatever your cadet does. My son visited Thurs-Sat. He went to meetings w/ coaches and attended classes. He was allowed to watch practice, but not participate. He went to meals. He hung out in the evenings w/ his hosts, who studied some and played some. There are cadets who study constantly, but there are plenty of cadets who are "chill," and study only as much as they deem necessary. Have fun!
PS: bring money for USMA merchandise at the cadet store!