Clearly, its more the over proportionate amount of party nights that will make those 2 nights a week hellacious. But the extra hour only compounds that further.
It certainly isn't going to help- check out the wait times at 7pm this December 11th and let me know how it looks.
The bottom line is- are you a family that chose to go to Disney on a slower week in December- say, the first or second week? Were you wanting to watch Happily Ever After? Cool- pick one of these 2 nights and prepare for it to feel like crowd levels that will rival the 4th of July fireworks. It sucks for them- you and I go enough that we can effectively tour around it