IOA has no scheduled EE during our 3-day trip later this week, only USF. Is it worth it to spend time during USF’s EE one of our days in line for Hogwarts Express in order to be inside IOA right at opening? Or should we bail on USF EE one day and just very early RD IOA regular opening instead (it kills me not to take advantage of an EE tho)? I’m not even sure if they let you “enter” IOA via HE at opening. TY in advance!
Not if your goal is to beat the crowds to Hogsmeade. The first HE train will arrive slightly after the guests who came through the IOA main entrance.
You can enter IOA main entrance a little early, and are held at Seuss Landing until 10 minutes before official opening time.
Personally I think you’re better off taking full advantage of early entry in USF and then head to Hogsmeade in the afternoon after the morning crowds clear out. Or if you have had your fill of USF, then skip EE and go to rope drop at Seuss Landing as @bebe80 suggests.