It's probably worth doing this. I checked my receipt and order details and there is no mention of "you must use this code by xxxx" or any sort of expiry date. I was curious so I did a search online and found a couple of people asking the question only to get "just register it and it will add on to your existing sub duration." which wasn't an answer. There are a couple of questions on the Amazon purchase page asking "how long does the code last if I don't register it", and amongst the "just register it, it will add on" replies there were a couple of "it will last forever", which I doubt is true.
I would say if you're planning to buy the sub now while the deal is on, but not going to activate it for 3-6 weeks, you should be fine. If it's more like 3-6 months, I'd say either wait for November Black Friday, or contact Amazon to see if there is an expiry on the code. As they get them from Adobe, I would imagine either company would tell you, but Amazon seem to be more responsive with queries - plus it's them you're going to go to for any refund if anything doesn't work..