Thanks for the good info!
I need to get him to understand that the computer is not his and shouldn't be the focus of the visit, which it currently is. Thus, like you said, when he can't use it, it throws him into a tizzy.
So, I'm thinking at this point of giving him a time limit like:
Friday, they gets to my place at about 6:00 and 9:30 is bed time, so Friday night night, 2 hours on the computer.
Saturday, he's there all day, so six hours.
Sunday, they leave at about 3:00 PM, so 4 hours.
Sound reasonable?
Again, I'm not only new to Asperger's, I've never been in a "father figure" role either.