I have the same issue. My cham does not like to be handled. I'm working on it though. I've found that feeding by hand seems to help, when when you can get them to take the food from you. :D
I dont think anyone can give you an exact answer. I wouldn't let him go more than 4 or 5 days without eating anything. But if you stick to your guns, i'm sure he will start eating his staple food. Good luck and keep us posted! :D