Depends on the individual snake. Personally I tend to wait until the feeding lump has moved right down the snake, and for a couple of my adults that stay in feeding mode and want to kill me after they've eaten I might wait 20 minues or so for them to calm down.
As for the pooping, they go when they need to, sometimes right before or right after feeding, stimulated by moving around. (Which is probably the poop from the feeding a week or so previously)