IME this is what happens: You get the "we're still trying" email at T-5 (usually about twenty minutes after the window), then nothing (and I'm not sure how often the system checks, but my guess would be T-5, T-3, T-2, and T-1) until the "we're returning your SNAs" message at T-1. If the upgrade clears at one of these checks, you'll get the suite confirmation email shortly after it happens (maybe about thirty minutes after the window) and the suite would show on the reservation the the SPG website, with reference to the original room category removed.

With SPG, the rules were explicit that you would be confirmed into the highest available suite of the categories you checked. Nevertheless, my SOP was always to check only the suite categories I really wanted at the beginning of the year (for instance, no junior suites for me as I didn't want to waste my SNAs on them) but as expiration approached for SNAs or if I had a small number leftover before I earned the new set, I would get more liberal about the room categories I was willing to accept.

Because of the categories, I prefer to request SNAs myself online as IME Plat Concierge phone agents didn't seem to understand this and would check all categories automatically, not understanding the instruction or why you were asking which categories were possible.

Since the merger, I'm not convinced we know that the system automatically confirms the highest available suite category.

BTW, some (few) properties include large family rooms in the SNA pool, so be careful you don't check these unless you want a room with three beds or bunk beds.