Halloween at Universal Studio Osaka

Hi, I am considering revising my itinerary as I just realised we will be in Japan during Halloween and would like to visit USJ Osaka on Halloween. I will be travelling from London with an 18 yr old and 16 yr old. Our flights are booked round trip London to Tokyo. My earlier itinerary was as follows:
Day 1-3 Tokyo (Shinjuku/Shibuya)
Day 4-6 Kyoto
Day 7 (31st Oct/Halloween) -Kyoto to Hiroshima -stay overnight at Miyajima
Day 8 - Spend some more time in Hiroshima/Miyajima and leave for Osaka. Stay in Osaka
Day 9- Osaka
Day 10-Osaka to Tokyo (Asakusa area in Tokyo) morning
Day 11-Day trip to Mt Fuji/Kawaguchiko from Tokyo
Day 12- Free day
Day 13-early morning flight back to London

But now, I would like to go to Osaka from Kyoto on Day 7 (31st Oct) as its Halloween and we would like to check in at hotel in Osaka and head to USJ first thing. I would like to know the logistics of this please. We are staying in a hotel in Dotonbori. Is it doable to go from Kyoto to hotel in Dotonbori and then head to Universal and then return at night to hotel after Halloween events in USJ? I will buy USJ tickets in advance but obviously cannot be there really early as we will be travelling from Kyoto.

More importantly, any suggestions please how I can then revise my itinerary to include Hiroshima/Miyajima and back to Tokyo, include Mt Fuji, and stay at Asakusa, and have one free day before heading back home? I had originally planned on staying 2 nights in Osaka, but now I am wondering if one night is enough (day 7) and next day around noon we head to Hiroshima, do the peace memorial and A Bomb Dome and Museum in Hiroshima and move on to Miyajima (Stay overnight in Miyajima) and return to Tokyo on day 9.

I have hotels booked (refundable) so would need to change or cancel if I am changing my itinerary which is not a problem, but would like to get a grip on how best to do this.

Many thanks!

I am absolutely no expert on Amusement Parks. However all I hear is that being on site as early as possible is key. And you seem to think the same.

Thus why not reorganizing the entire flow:

Day 1-3 Tokyo
Day 4-5 Hiroshima /Miyajima
Day 6-7 Osaka stay in a hotel close to USJ
Day 8 - x Kyoto
Day x to end Tokyo

Thank you so much likebike for replying! Certainly considering this.

I went to USJ last September. We didn't arrive until 11am. No entry lines. Straight in. Busy as usual inside.

Hi H, good to know!!! Halloween week might be a bit different though.

Maybe. We had other visitors dressing up in Halloween costumes and the extra shows.

Lots of visitors arriving around 4pm dressed up.