All flock should be fine. I think medicated is only recommend for a few weeks anyways. We never used medicated just switched back to grower (all flock) when we added the new young ones.
11pm is way to late for bed time. My go to roost between 8 and 830 just as the hue from the setting sun...
Don't depend on ziggy to protect the babies. I had an older pullet take in young pullets for a while too but when we added more to the flock she wanted nothing to do with the baby chicks. Just because they mother once out of companionship or stress doesn't mean they will mother every chick that...