That's one of the biggest issues in feeding hens: When to switch to layer feed. Just by going by weeks of age is not always the best method to decide. You say you have Delawares, and those being classified as a Heavy Breed, it would be best IMO to keep them on Grower until the eggs get to about 30-40g each. Our Delawares aren't the most prolific egg layers in our flock, but they do produce avg egg size of 60g which is a good sized egg. One thing we've noticed is that when chickens begin to start their egg laying cycle for the first time, its best not to adjust too many things, i.e. change feed type, move hens to different house, lighting adjustment, etc. This may stress them out and delay egg production. After all, this is egg laying thing is new to them, so make it easy as possible for them to get used to doing it every day. We have our feed mixed in bulk, and we keep Heavies, (Delawares) on our 22% grower until +/-35g avg egg size, which is usually 26 weeks I'd guess. If you have only a few chickens, it would be ok to keep them on grower indefinitely, seeing how your feed volume isnt that high. When you feed 5000 chickens, protein is $$$. So you have to watch the protein levels, not so much for egg production, but mainly for costs. If money were no object I'd feed grower throughout, and supplement with oyster shells to all my chickens.