I don't get time during the day so I do most of my technical work at midnight. I leave my computer on for 6-7 hours for no reason at all, and I my self am on 3-4 hours...well not at a time, after 30 minute breaks between each hour(to compensate my lack of rest). The longest time I've spent on my computer however was when I had a very important assignment and lots of work agh...it was a real nightmare...
...15 hours in one go I believe...
...
And casually I believe the longest time was 10 hours...I made 100 animated gifs....[what!? I was bored...]