What is a good amount of time to wait to check up on a recommender after the initial request?
I would definitely not contact him until the week before the week he said he could get to the recommendation letter. Anything earlier could just lead to the same answer as before. I wouldn't stress it too much, however. My recommenders this year submitted their letters within the last two weeks of the deadline. One of them submitted it two days before the Thanksgiving break (at the end of which, some applications were already due).