Erin, that's quite interesting. Maybe I'll actually try to leave next time too, just for kicks to see what might happen.
Lychee, I can only tell you of my own experience. I have not done any formal study on the subject, but I have experienced it first hand hundreds of times, if not more. Usually it happens to me 20 or 30 minutes after I fall asleep. It doesn't matter if I've gone to bed for the night or if I'm just taking a nap. My method is probably not one that can be taught easily, but it's definitely easy to perform. If I ever want to do it on purpose (which is rare) all I have to do is just to have the thought "I'll do it tonight." Then it just automatically happens about 85% of the time, 20 or 30 minutes after I've fallen asleep. I seem to be able to make up my mind when my body is asleep. From there, I can induce the vibrations, dream, or think about something very deeply. Do you ever wake up before you actually open your eyes? If you can do that, you might have an easier time. Also, there are mp3 files that you can download that are supposed to help you induce OBEs. I only tried it once and it worked. There's probably a few more methods that you could find by doing a search.