Hyatt reps can always be confident until something happens then all they can say is “whoops”. Happens all the time with SUA’s, GOH’s, and many things sadly. Since this is the first year these have existed I’d say it’s only just best guesses.

From my own experience they’ve credit to the day the stay posts, not the checkout date and the entry on my Hyatt earned date shows that in the record too. But who knows that’s why I asked and hopefully there’s some DP’s.