For the other chicken feed, check the label.
No matter what they call it, what you really want for chicks is protein between about 18% and 24%, with calcium under 2%, and instructions that say "feed as the complete ration..." for any age of chicken (or even duck, goose, turkey, gamebird.) If it meets all those points, it should be fine to feed for as long as you like.
If it has less protein, it is a bit low for chicks.
If it has more calcium, it is meant for laying hens, and long-term feeding will be bad for chicks. A meal or two would not hurt them, but eating it for several weeks certainly might.
If the instructions say it's a treat, and to limit it to a certain percent of the diet, it probably has a badly wrong amount of some nutrient (low protein or high fat are the most common problems with treat foods, but not the only possible issues.)
