We attended E-night on a Tuesday last June. It ran from 10pm until 1 am.
We sat in the eating area outside of Tomorrow Land to watch the fireworks and then proceeded to Buzz and then Space Mountain. We had really no waiting time for either. After that we went over to Big Thunder and the crowds starting getting larger, but still not bad at all. It was a lot of fun but we were really tired as we left the park around 12:45am. It is certainly worth it, but make sure you take a hotel break before starting E-night.
Enjoy!