I'm interested in your question, but I'm not sure what you mean by "late," neverbored; and I'm afraid I don't have any specific suggestions about night owls. They're out there. I tend to prefer the late side of things, say 11:00pm-1:00am, and I've never had a problem finding someone for that time. But maybe by "late" you mean "early"--2am or so. The pickens do get slimmer. I'm sure you know the agencies who have availability until the wee hours. The independents are more reluctant to book really late; I haven't had any problem with 10:00pm or 11:00pm, but after that they're less likely to be available (fair enough.)
More generally, I know that many out here like to see women at the start of their shift (?), when they're "fresher." I get that, but I actually like being their last call, when they may have more freedom to relax, have a few drinks, and extend the session if it's going well. Booking 2-3 hours seems to help. On the other hand, I have certainly had companions who are tired and ready to call it a night.