Generally speaking it depends on the female.
I've had new mom's I can get right in there while she's having them and she's fine. I have also had new mom's that if you drop a rat pellet into the tub a week after the babies are born she'll kill them all. needless to say, those moms get fed off.
For the most part, if your females are used to you before they have babies, they'll be cool with you afterwards. It's good to check on the babies once a day. My favorite trick is to give the mom a super-nummy treat and when she goes to eat it, I do a quick head count and then let mommy check me out to make sure I'm not removing any babies.
Gale