I went to the MK extra hours in late January on a night when MK closed at 8pm. A few notes:
1. I got to the park at 6pm and it was crowded. Lines for nearly everything were pretty long. I wanted to have dinner at Columbia Harbor House but they closed at 6pm! Check those times and make your mobile orders early. I ate at Pecos Bills, which was very crowded, and the food wasn't wonderful.
2. I got in two rides before 8pm--BTMRR (LL) and PoC. I got a sundae to eat during the fireworks then headed into Buzz at about 7:50 (walk on).
3. At about 8pm I wanted to ride on Pooh but there was an extremely long line. Part of the issue with the line was people arguing with the CM about their eligibility to stay late. One CM and a bunch of guests disagreeing about whether their hotel was eligible made a real snarl in the line.
4. Skipped Pooh and walked to HM, which was almost a walk-on, then PP, which had a 10-15 minute wait, then back to Pooh for a 10 minute wait. During this time SDMT consistently had a 40 minute wait. If it had been a walk-on I would have grabbed it.
5. Things that were not open late: Princesses and People Mover, both attractions I wanted late in the evening.
Complaints: too many people hang around after 8pm who aren't eligible to stay late. The park was a mess by 8pm, the queue for PP was filthy, with piles of garbage along the queue floor. Less food service available late.
Compliments: cast members were great, and friendly, as always. No ride breakdowns when I was there. Disney transportation seemed to be flawless and got me back to the TTC quickly (express monorail).