As the PP said, HalloweenTime is slated on September 7, 2018 (Friday). I think both days will be crowded, but if I had to guess, I would guess that Sunday 9/9 will be busier. The 9th is the first Sunday after the start of HalloweenTime, which lately means a lot of locals (AP holders) will be in the parks checking out the decorations, overlays, merchandise, entertainment, etc. Sundays are also generally busy because only the SoCal Select AP is blocked out. On Saturday, the SoCal and SoCal Select APs are both blocked.
In terms of evening entertainment, usually fireworks and F! drop down to a weekends (Fri-Sun) only schedule once summer ends. (On Fridays when there is MHP, F! is not presented and fireworks are only presented during the party.) Saturday and Sunday should have the same evening entertainment offerings. As mentioned, WoC would normally be presented nightly, but they've announced that it will be down until later this year. They haven't said anything about the Pixar Play Parade or Paint the Night. I would keep an eye on the dining packages for PtN and the Pixar Play Parade as a preliminary way to see if the parade will continue past Labor Day (right now, the dining packages are available through 8/31).
I called to ask about when HM would be closed for the overlay and was told it would be down for a week in early September. The CM said the park would not be fully themed until the first MHP on 9/19. What do you think? Is that just the CM having no idea? I’d hate to go and not be able to do HM with the overlay.
The
Disneyland webpage for HMH says it'll be returning on September 7, 2018. I'd be inclined to take what the phone CM said with a grain of salt. HMH has, historically, taken 18-days to install. So only closing for a week would be quite a change. Space Mountain Ghost Galaxy only takes a few days (<1 week) to install, so perhaps the CM was thinking of that overlay.
