the answer is silver. ua does it on status at time of post. i'm amazed other airlines would back date it. which ones are those?

rdm and eqm simultaneously post. normally it's 24-72 hours in my experience flying ua ac et oz nh lh. tk and sa are a week or so but that's tk and sa for you.

i'm pretty sure you can call the mileage plus center and have it adjusted if the additional multiplier makes that huge of a difference to you, that is:
you fly saturday 1000 miles (qualify for gold)
you fly sunday 9000 miles

sunday miles post monday at the silver multiplier (getting you gold)
saturday miles post tuesday at the gold multiplier

you want sunday miles to post at the gold level and understand saturday miles will post at silver value.

yeah gl explaining that succinctly to them. let us know the result cause i never bothered doing this