With new snakes I personally keep handling to an absolute bare minimum until they have eaten 3 consecutive meals without refusal.

Like redshepherd said, it varies by animal, beyond that. I stick to a basic "guideline" of keeping handling sessions short and sweet at the beginning and gradually increasing frequency as well as time of handling sessions. To elaborate a bit, I start out with maybe 10-15 minutes max every other day to every three days for a few weeks and then increase gradually depending on how comfortable the particular animal seems to be with handling.

I also should mention that I don't handle while the animal is in shed or after feeding.