When we went in October, it was not as crowded as it was during the day. There were still some wait times but not bad at all. It was worth it, for us anyways, to go to the late evening hours. We prefer to do this than go to the morning early hours.
I was wondering this too. I'm worried it'll be to busy and not worth it. My friend did the evening emh in July and said it was great, so I'm guessing it's not too bad.
It really depends on what you want to do. We did EMH in Epcot last week so we could do soarin' w/o too much wait. Well, everybody was in line for soarin too. And with no fast pass available we decided to do it later. So we jumped on the Living with the Land ride and headed over to Living Seas. We ended up doing Soarin' with the Fastpass later on in the week. EMH at MK are a little better b/c there are more rides open and it splits the crowd up, from my experience. Have a great trip!