when should chicks perch?and feeding.

My bantam hatched 2 orpington cross chicks on Aug 1st, they're doing really well and now shared with my other bantam hen.When should I close off the nest box and persuede them to perch or do they still need Mum's warmth at night?
Also as they're now always a foursome I've given up trying to feed seperately and put layers mash and chick crumb in the same feeder, is this going to be detrimental to hens or chicks.
So much to learn but loving it!