There are some BP's that will only poop after a shed so there is no reason to wait to feed until then.
For young BP's I feed them every 4 days. Once they get up to 500-600 grams I move them onto an 8 day feeding schedule. 4-5 days is the minimum amount of time between feedings, as it takes a day or so for them to digest.
For young BP's I feed them based on weight. 10%-15% of the snakes body weight in rodent.
So a 100 gram Bp would get a 15 gram rodent. (100 x 0.15 = 15)
For older BP's you want to feed a rodent that is about the same width as the widest point on the snake. (this also works for young BP's)