No matter when it is, just don’t make him totally nuts. It’s not worth it FOR EITHER OF YOU. He works hard during the zman and probably uses bain hazmanim to “chill out” a little bit. I think it’s YOU, THE PARENT, that needs to relax.
As for the for the poster above who mentioned that in their house the bochur went to work with Daddy, that might have been the case but over the years BH people are realizing more and more what Chol HaMoed REALLY is…. YOM TOV, and more people are talking off of work then ever before. Granted if you want a business that requires you to stay open because of Chol HaMoed or Yom Tov, you don’t really have that option.