I spend several hours per day on my PC but to tell you how much of that is towards my IM business is a different story.
From my main site + my 1 or 2 niche sites, about 3 hours a day. I make around $300 a month. I'm new to this stuff : D
I usually work 12-15 hours per day and am making about 2K a month. I work those hours happily though, as long as I don't have to get a j-o-b.
Just started. Due to me having a 9 to 5 I cant put in more than 4 hours per day, but Im already seeing results~!