They're constictors, right? It's hard to constrict a chunk of salmon. I don't think it would hurt the snake, but I'm not sure you get could really get a proper predator response from an animal that's designed to go after small warm blooded fuzzy things.
You can spend plenty of time with the snake, but I don't recommend doing it right off the bat unless you got lucky and got a super-friendly one that's already used to humans. First week you usually don't want any real contact, just check on the temps and clean the tank and make sure everything is okay. Second week you can start the 20 minutes every third day or so thing. If she's really into handling, you can handle her more often. But if she's shy (curling into a ball, hiding head, not exploring, exploring only to immediately hide) or stressing (defensive biting, tail-wagging, constant hissing, peeing or pooping on your) you want to limit the time. (But I don't put them right back after peeing on me or biting--I don't like them to associate those behaviors with getting their way.)
I actually got more than one ball python partly so that I could alternate snakes and handle one every day without worrying about stressing them. Now I get the idea they'd all like to come out MORE often then they do... ball pythons that have been around you for a year tend to be pretty okay with frequent handling. Even if they started out totally neurotic.
But don't handle for a good two days after feeding. They really do need to digest in peace, and even the friendly ones will just be sluggish and boring. Oh, and the middle of the afternoon is snakey nap time. Early morning is okay, but evenings are best.