Start now. Go to you tube and search “kitten lady feral moms” for tips on how to handle and socialize babies with a feral mama.
A long handled big wooden spoon or spatula is a useful tool. When the babies are little you can just scoop one up on the big spoon and bring it towards you while maintaining a safe distance from mamas claws. When I had feral mom + 4 babies last year I also got some thick elbow length leather gloves which came in handy. Mom might mellow out as she starts to associate you with food. I had them in my garage in a huge dog crate. Feral momma got used to me feeding and cleaning and taking her babies into the house for playtime and socializing. I think she even enjoyed the break when her kiddos got older and more rowdy. She never warmed up to me or wanted to be a pet, but the growls and jump scares stopped.
Congrats on joining the kitten care-taker team