The best time to practice is in the morning, when you are awake, refreshed and not likely to fall asleep. I mostly practice Saturday and Sunday mornings because I can sleep in late, wake up refreshed and then have plenty of time to practice. I also recommend you take a nap sometime during the day, and use that time to attempt to leave your body. Naps are better than bedtime, because you're usually not as tired. You can relax and really get into it, without being so tired that you just fall asleep right away.
Some people believe that OBEs are the same thing as lucid dreams.
It's easy to confuse the two. I'm not an expert in the field of lucid dreams, but I can offer my opinions. It is possible that these experiences are actually OBEs. Scientists have developed a few commercial devices that monitor the eyelids of a dreamer. When REM sleep is detected, the machine flashes a light or sends another signal to the dreamer.