It really varies from snake to snake. Some will stop eating as soon as the season begins, other will eat until they ovulate. Most of the time, they all stop eating after ovulation, but I have heard stories of some that eat even after that. I think that needs to be considered a somewhat oddity though.
Keep in mind, just because they aren't eating, doesn't mean they are in fact gravid. Balls go off of feed for so many reasons, that it can be misleading. Watch their behaviors and their sheds and see if it all adds up.