IMHO you will do better by consistently sticking to a schedule, regardless of the time of day.
But, that's not to say that certain times of the day won't be better or worse for you. I'm on the east coast and I've found that being online from 11PM to 3AM tends to be the most lucrative for me right now. It means being up really late my time, which a lot of girls don't necessarily want to do on this side of the US, but being a night owl, this benefits me. But, when I started, 8PM to 1AM was much better, but after 1AM I wouldn't make nearly as much.
There are a few things to consider:
-When do you have the most energy?
If you're not a morning person AT ALL, trying to force yourself to be upbeat at the break of dawn when you're just not might be counterproductive. People go on MFC to be entertained, and if you can entertain at one hour better than another, that should be your focus.
-Where is your placement on the page?
If you have say, a 2000 camscore, you might get lost when a lot of popular models are online, but if you are on when a lot have logged out already or aren't on yet, you'll be higher up on MFC's page. This could very much be to your benefit. As PlayboyMegan mentioned earlier in the thread, if you're on during the day and you speak English really well, try going online then. You'll definitely have a market, use your tags wisely.