When I take trazodone it takes about an hour to work. But for me it doesn't work in an entirely different way. I'll sleep for a couple of hours and then be AWAKE for a couple hours.

Like kaliope said, how much caffiene do you drink? How long have you been on this "nocturnal" sleeping schedule? If it's been a while it might take a long time to get your body used to a different schedule. It'd be like moving half way across the world and have to immediately adjust to the new schedule.

Maybe a first step would be to try to adjust your wake up time if that's possible. Going to sleep (for me at least) I have almost no control over. But if you could start getting up earlier and earlier you're still getting some sleep and hopefully the bedtime time would just naturally follow. Perhaps?