One of the things that never ceases to amaze me, is home much time actually goes into "quick adjustments." I'll be working on a level and I'll be close to the end and think that if I just make a few little changes here or there I can consider the work done. Its usually seemingly really simple work (just adjusting some numbers) and then suddenly two hours have vanished. I never felt the time pass by but it's gone all the time. That's game design in a nut shell. When you are working on something, even the stuff that might seem like the quickest changes you can make suddenly take forever whether you realize it or not.
Last night for instance I was working on creating fog to cover the land in REDkit for a level I was creating. It wasn't the quickest change, there are a lot of things that need to be adjusted in order to get that effect but I figured I could at least get it started. Wasn't really planning on spending anymore than about 45mins doing it before calling it quits. Fast forward to 3 hours later, I'm still scouring the internet for tips and tricks I can use to make the fog look better. This kind of crushed any sleep I would have gotten last night so needless to say that I'm currently exhausted but I hate leaving things undone. Its something I've actually tried to do before: quit, shut off my computer, went to bed, only to get up half an hour later because I had a new idea and I needed to do it "right away."
Moral of the story: Sleep and Game Design aren't friends. But if it's what you really want to do, you will have a blast.