I have delayed sleep phase disorder and sleep at random times. I'm freelance though, and my deadlines are always 9AM. And I'm a procrastinator, so I always work at the last minute. So if I have 5 hours of work, I wake up at 4AM, and usually go back to sleep again at 9.
I've been using alprazolam for sleep for a couple of years, cycling it with melatonin and sometimes diphenhydramine, which seems to have stopped working recently... Luckily I have maintained the same alprazolam dose (0.25-50) and am always able to take breaks.