Depends, there is to many variables to answer that with just one description. Right now I am enrolled in school and take a few online courses. Day's I have to study or work on something, I am on pretty much the whole day aside from work. And with it being winter pretty much here in Pittsburgh, I spend any free time I have after that on the PC playing games, reading news, watching movies and so on.
When the weather is nicer the amount of time I spend on a computer is greatly declined. I still watch movies or play games, but I love the great outdoors. And sure, I have a laptop, but it kind of defeats the whole " going hiking" thing if I lug the PC with me in my backpack.
It also depends on who it is that whats to know, how much time I spend on a computer. Someone say, my grandfathers age who didn't grow up in a digitized age would probably say I spend way to much time on one even if it was only a hour or two.
With computers being able to do so much, and with the endless information on the internet, it would be easy for one to spend a life time on a computer. I like others, I am sure, have been bored out of there minds and stumbled across something on the net, that even though it was retarded and pointless and provided no real interesting information at all, still have looked at are watches or the clock and said " It's 3:30 am, what the hell have I been doing the last 6 hours...?".
I am easily amused. I've googled something and found links to message boards that have no more then 20 members. They just so happen to have a topic of what I googled. I read it, was amused, and sign up just to reply. If they are on and reply quickly, I could spend an hour easily arguing with a user " who is probably 9 or 10 years old" about anything from a video game, a movie, to politics. Well, if I am really bored that is.
So to answer your question, to much time I guess.