Well said already by everyone. You never want to hand feed if you have no experience, but if you ever do learn then yes, pull them between 2-3 weeks old, no older. Same for just handling them, if you're letting the parents feed them but you want hand tamed babies you must handle them every day for at least 10-15 minutes each from 3 weeks on. Much older and it's tough.
As said you have to block the entrance to the box when dad and mom leave, then get the babies out on a towel or blanket and handle each one for 10-15 minutes at least. Scratch, hold, play with, talk to. I'd start now because 27 days old is already pretty late.
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