Just adding to the data point:
I upgraded Premier Rewards Gold to Platinum 3 days before I need to get on a flight with my dog. Flight was on 12/9 and received credit on 12/12 for $117.72 (It was CAD$125 as I was flying from Canada back to US).
Bought two $50 eCert on 12/15 with the following posting
From: LOS ANGELES INTERN
To: LOS ANGELES INTERN
Passenger Name: PASSENGER/DELTA
Document Type: PASSENGER TICKET
Received credits on 12/17 for $50 and $32.28 (which is the balance of my $200 after the above pet credit). So it worked out great.