I wait until thei eyes are open and they are very active; what could be called the "rat hopper" stage. I make sure to see them all eating solid foods, and able to drink from the water bottle; then I just remove the mother into a cage that it without earshot or sight from the babies. It is no that difficult

I have had to "emergency wean" babies that were a tad on the young sige before. They still had the "dim" look with their eyes noly partially open. I used moistened lab blocks and made sure that they knew how to use the water bottle, and they were fine. This was in the case of a mother that died while nursing; but the babies were fine.