If you're only feeding layer, it's supposed to have enough calcium for laying hens. I've never tried it, though. I range mine some and give them kitchen scraps and some of the garden overflow... I find that they will self-regulate their calcium intake if I leave the shell available.
I am using a non-medicated grower feed and there is no need to switch to layer other than my preference for pellets. So, I switch when ALL are laying. There are differing opinions on feeding layer to roosters. Some would use an all-flock or grower feed while others insist that the excess calcium won't really harm an adult chicken. You'll just have to decide how you feel about it. Layer feed was developed with the commercial layer in mind and there obviously aren't roosters in those facilities.
I am using a non-medicated grower feed and there is no need to switch to layer other than my preference for pellets. So, I switch when ALL are laying. There are differing opinions on feeding layer to roosters. Some would use an all-flock or grower feed while others insist that the excess calcium won't really harm an adult chicken. You'll just have to decide how you feel about it. Layer feed was developed with the commercial layer in mind and there obviously aren't roosters in those facilities.