Not being able to move, and sometimes experiencing "vibrations" (among other completely harmless hallucinations) is characteristic of sleep paralysis. Sometimes if you're really tired or have a wonky sleep schedule, you can end up sometimes waking up into it, or going into it before falling unconscious when you're going to sleep. As for the time-setting itself, I've done it a couple times by just affirming to myself that I'd wake up at "X" time, and ended up waking a half hour or so earlier.