My understanding of the OP is that the OP is talking about two different things? One thing I think that is being asked about is the 2 elite nights credited for every 5K spend on the WOH CC? For those, my understanding is those nights post on your monthly closing date of your CC (mine always post the same day every month, regardless of when I may or may not have hit the 5K threshold in spend). If my understanding is correct about when those post and the need to have those posted in 2021 for qualification, you will need to make sure that your monthly closing date is as close to 12/31 as possible to maximize your ability to get the elite night credits based on spend. I have read on here and around the interwebs that sometimes if you contact the CC company, you can change your closing date to help make it easier for you to get those elite night credits.

The other thing being asked about I believe is the extra FNA that is awarded for spending 15K from your 2021 AF date to the end of the year. My understanding based on the published T&Cs is that will be calculated purely on spend up until 12/31, regardless of your monthly close date. However, i don't believe that the FNA will post to your WOH account mid-cycle, and they will just wait until they post everything else. Just my thought, but I am going to message Chase and I will ask about that as well too.