DME & on-site? You wouldn't arrive at your resort until at least 1:30pm (or later). What about flight delays? Room may not be ready. Then an additional 1 hour to arrive at MK (Disney transportation). Lunch/early dinner? Need to consider this too. What time would your day start? This factors in too. Guests can enter at 4pm. To maximize your party time need to be there early and stay to close, IMO.
I definitely understand your excitement & attending with adults should be better than having kids, but too many what-ifs for me. Enjoy your arrival day, maybe go to another park. Have a fresh start for the next day.
Thursday vs Friday hasn't necessarily been the case for MNSSHP; same as watching 2nd parade vs 1st parade. It's like everyone took this advise. Ha! If you have a plan, and can be flexible, it doesn't matter which night you attend. I've only attended SOLD OUT parties for MVMCP & MHSSP, due to time of travel, and have never had a problem accomplishing what I want to, with DD under 10 for the last 4 years. We've met tons of characters at both parties. Happy planning!