How long to let a 10 year old play xbox during summer?

How long would you have a 10 year old play Xbox in the summer or what type of a schedule for him to play Xbox?

Right now he has no schedule and he is on it all day long unless he has baseball or if a friend comes over and they play outside. He does not need to be on it all day long its way to much and he is starting to act like a brat! Especially when i come into his room and ask him something (like what do you want to eat)? He gets snappy with me because im talking to him during his game!
I need to set some sort of schedule like play for 2 hours in the morning and then not again until after supper and has taken a shower and brushed his teeth? I really dont know so any input would help me out! So please help im in some dire need of a schedule!!!