If the feed is non-medicated, you could feed it forever. I suspect, however, you are asking what are the next steps. There are many programs, suggested by the various feed companies. If you are strongly committed to Brand X, I'd take note of their feed tables, or feed schedules. All feed companies produce these charts. They have them on their websites and sometimes print this right on the bag. The choices of sequencing and feed options are HUGE. Lots of folks feed Starter, and if they are hens, switch them to Layer at the egg laying time. Others, feed a product that everyone in the flock, chicks, adolescents, adults, males, females, birds not laying for moult, can eat. This just makes life a lot easier. This method requires the calcium source, just for the layers, is provided by offering shells on side. This is probably information over load, but frankly? The answers are varied and the choices and options are many.
Fred's Hens has a lot of good advice, as usual. By far the easiest thing to do is switch them over to layer feed around the time you expect them to begin laying eggs. At our place, that's around 19 weeks. You'll be feeding starter to your chicks for quite a while yet.
Feed your chicks grower feed at about 5 weeks, the back of the bag at your local feed store should tell you how the feed type progresses. i bought Dumor starter, then i bought grower finisher and just today i fed my 6 chickens Dumor Layer crumble to 18 week old chickens from tractor supply store.
