You only need chick starter (and sometimes labeled starter grower) for the first 16 to 18 weeks for layer type chicks. Then switch to layer feed at point of lay, which is 18 to 20 weeks.
Most importantly it should be 18% protein throughout chickhood shifting to 16% to 18% protein layer feed with about 3.5% or more calcium at point of lay or offer all flock 18% with oyster shell or calcite grit.
Do not switch from chick start to what is called meat grower, or a high protein grower, as that will be 22% protein which is far too much protein for layer types and can mess with joints during growth. (It can force them to grow too fast or put on too much weight too quickly)
The regular chick start is fine until they are ready to lay, or ETA: as aart stated, you could finish out the 50lb bag at point of lay by adding oyster shell or calcite grit as long as it is non-medicated. You actually can eat eggs from hens on Amprolium the med in medicated feed to stunt cocci overgrowth) but generally you want to get them off of medicated by point of lay so their own immune systems take over.