Everyday Dad,
Take Joes87 post and read it to your son. He is pretty much spot on as far as the time commitment required. My son routinely goes to bed between 2-3 AM, as he does not have an early lifting, but I think during the week he functions on 5-6 hours sleep. Quite often on a Friday night he will be up in engineering lab working on a project.
That said he does go to parties from time to time. His team has a "baseball house" and they hang there sometimes. His "fraternity" is the team. He has a girlfriend who is also an athlete and they seem to find time for their path's to cross. 
In addition to what Joe pointed out you also have the commitment to summer baseball, so your son will likely only be home for the holidays and for a week or two between summer ball and back to school. It is both a grind and a unbelievable experience and he would (and most who really love the game) would not change for the world. A lot drop out during the process and my son lives with an ex player who dropped in his Jr year as he was not playing and had other priorities.
Good luck and I think it will help your son read through some of the posts in this thread.