I don't see it as that big of a deal. You can certainly check in (and you should) but you may not get your room until later, sometimes 4 or after. Hopefully your room will be ready in time to get it settled before your tea reservation. For us we'd plan to stay in the room until around 11 or just before, do an early lunch or late Breakfast close by and then go over to the GF. However, I'd likely go over early and check in then return. You might consider an 11ish breakfast at Whispering Canyon, GF cafe or counter service since it's al a cart rather than a buffet like chef Mickey's due to your mid afternoon tea. An alternative would be to have an earlier breakfast in the room then go to MK (if you have a pass) for a couple of hours, to play mini golf or just explore the resorts nearby. You could just soak in the ambience at GF during your down time before either your room was ready or the tea. I would add that for Marriott you'd be able to stay in one villa until the other were ready even if it was a different resort and I do think Disney could do this with no impact on room readiness.
