When I'm at work... Like right now. Not to say that I'm always able to get away with drawing at work, and I certainly can't paint there, but I always seem to have this overwhelming desire to paint when I'm busy with something else. But generally the time of day doesn't matter much to me. I paint when I get the time.
Probably not... at my last I had to hide it. Luckily I worked nights and there wasn't a supervisor around for most of my shift. Where I'm at now I can during slower times as long as I'm still getting my job done.
I am completely and entirely bound to the flimsiness of the urge to draw. It usually hits when I see something that immediately captures my attention -the profile of a face, a character I particularly like, a dress or costume I find interesting.. Most of the time what I draw is what puts itself before me to drawn, that's what it feels like. I don't go looking for it, and drawing's never about an idea for me.
Sketching in trips and visits is a particularly nice habit too. I have scrap-sckethbooks for museum visits, excursions in town or trips out of town. There's something about capturing your adventure in sketches that photography just isn't capable of.
personally i can draw best when i feel forever alone and/or sad (which is now T-T)