It really depends, sometimes zero, sometimes a few hours, sometimes what feels like 'all day' though it's probably 12 hours max (I hope?) or maybe 15?? (or anything inbetween..) and sometimes I do other things inbetween, not just hang online..
I wonder about people who clicked 'zero' - what are they doing here then??
And 'all day' - surely you don't mean 24/7, 7 days a week? (or could it be a WoW addiction??)
I almost don't watch TV anymore, I used to almost be 'addicted' as a teenager.. I might be addicted to the internet a bit.. probably need to work on improving things in RL, it can be a too-great escape, yeah..