It depends on the individual snake. My first 3 ball pythons all had no problem being handled for 10-20 minutes daily (besides feeding/digesting days) as babies. Some babies might be more easily stressed.
Just be sure your BP eats a couple meals first before handling at all. Then you can handle under 20 minutes, every other day. And go from there. I think the only real rule is not handle for too long per session.