I only really bot while I'm at the PC but that's normally around 8-14 hrs a day, although I'll leave a bot running unattended for a couple of hours if I'm confident it's a solid, non-stuck profile or if I have LogMeOut set with some stringent settings to protect me. Max 3 accts normally, doing a wide variety of things.
I was paranoid as hell for the 1st 6th months and only used rotations on my "main" acct, but now I bot just as hard on that, I've got duplicates of all the classes I care about on a "safe" acct on the same battlenet now anyway, so if I get banned I should just be able to reactivate that.
I'm starting to suspect that one of the reasons I've never had a sniff of a ban is because most of the accts are very old (used to multibox), but that's just speculation. Apart from that, also never had a single accusatory whisper or comment from another player, but I do try to "bot smart".
I don't tend to do any one thing for more than 3hrs before switching to another char.