Originally Posted by
MaxVO
There has always been a range for how quickly the airline selection updates! All other AmEx processes continue to be highly variable. It was a really pleasant surprise that the OP got lucky with the latest experience. But one DP does not translate to a change in expectations. It's BAU.
The OP's isn't the only DP. There have been several over the years of this happening and even more DPs of those that selected the airline, received immediate email confirmation of selection, and immediately purchased UA TB and successfully receiving the reimbursement (have done the latter myself many times and don't usually bother waiting 24 hours after selection). My point is that if you received the email confirming your selection there is no need to wait. But of course people are welcome to do so if it makes then feel more secure.
ETA: This doesn't only apply if one is aiming to use UA TB. The same would apply if one wants to pay for seat selections or luggage; there is no need to wait 24 hours after airline selection to make those purchases. A couple of years ago my dad had similar story to the OP. He paid for seat selections on UA and then realized that he hadn't selected UA as his airline. Immediately called and received the email confirming UA as his airline choice. Reimbursement for the seat payments posted as expected a few days later.