If it's just one hour and the wait times are 25 - 30 minutes, then can you really enjoy more than 2 attractions during the nighttime EMH? It's a nice idea, but I still think that EMH in the morning offers the guest much more value. You can see 5-7 attractions during the EMH morning at MK, and then you can leisurely see many more attractions (with shorter lines) afterwards.
You can strategize an EMH morning, early afternoon, and late afternoon.
With the evening version, what do you do? "Let's save Peter Pan and Space Mountain for EMH tonight." Only to find each with 30 minute lines.
Not saying it's a bad idea, it just doesn't seem as good as morning EMH, especially at MK.