It's possible to start learning hiding around mid 400s with high 40s discipline and no buffs - but it's hard and you'll be searched out most of the time before you can learn any stalking. I found it significantly easier around 530s with low-mid 50s discipline.

If you're a Barb, roar wail before hiding to immobilize them and prevent their searching and you should be somewhat okay the closer you can get to 500.