We are planning to stay on Wednesday, December 18 in one of the Disney hotels, that day Magic Kingdom closes at 10 pm and has extra magic hour from 10 to 12 pm.
How do they accomplish this? Do they empty the park and then fill it again with only hotel guest? Do they go from family to family and check if they can stay?
Whatever way they do, it sounds like a lot of hassle for them to achieve this. I called guest services but the lady didn’t have a clue.
Does any one knows? Thanks!
They scan magicbands at the rides to see if you’re staying in a resort. No resort, no ride. Most people will leave the park if they aren’t able to get on the rides. Of course Disney won’t kick them out if they’re still spending money on food and merch.
Thanks etrull77 that makes more sense 
Is it usually as busy as early extra magic hours?
They also have CMs with mobile scanners around Fantasyland, Liberty Square etc. They then usher guests not staying onsite towards the Hub; I saw some families being “escorted out” around an hour into the 2 hr EMH.
Oh ok thanks Nickysyme, so I guess is both
From my experience night EMH are busier than morning EMH. That said, I have not been to night EMH in a few years so it is possible things have changed recently.
My experience with evening EMH is that they are very busy. DH & I planned EMH at MK after dinner for our date night in 2017. We gave up after 45 minutes as the lines were quite long and the walkways were very crowded. I suspect it will be the same for you since MK is only open late a few nights per week during party season.
Thanks BoilerMomPharmD and davej, maybe I should give up on the idea of keeping the kids awake that late, if it will be that busy with such a long waits.
Not sure if it’s an option for you, but when I was at WDW in October, the early closing party days at MK had very low crowd levels compared to the late closing non-party days. We got a lot accomplished by Rope Dropping MK on party days twice. We went back to MK late afternoon on a non-party day and the difference in crowds compared to the afternoon on the party days was dramatic.
Edit to add: Just realized you will be there during Winter Break so the crowds will be higher everywhere.