Look on the feed bag. Does it have a chart on it saying when to feed what? Many brands do.
What is the percent protein on that feed? It should be on the label. Some companies produce a combined Starter/Grower intended to be fed from hatch until they go on Layer. It's usually around 18% protein. Just based on the name I'd think that is one of them.
I've had chicks 5-1/2 weeks old go through nights in the mid 20's Fahrenheit. They were brooded outside and exposed to cold temperatures so they were acclimated. That makes a difference. But basically once they are feathered out they are feathered out. Usually that's around 4 to 5 weeks of age. That's for cold climates.
I watch my chicks to decide what to do as far as temperatures. If they are cold they will be huddled as near the heat as they can get and will probably be giving a plaintive peep. Once you hear that peep you know something is wrong, it's heart-wrenching. If they are hot they get as far from the heat as they can get and will probably be panting. Panting is how they try to cool off since they don't sweat. Mine tend to sleep in a group in a warm spot. That's not because they are cold but because they like to be in a group when they sleep. That warm spot is probably a habit from when they needed more heat.
In one ridiculous (for us) heat wave a few years back (+110 F during the day, in the high 80's to low 90' at night) I turned daytime heat off at two days and nighttime heat off at 5 days. This was in my brooder in my coop. Their body language told me they did not need it and they did not.
I've had broody hens wean their chicks at three weeks, left them totally alone to take care of themselves day and night. I'm guessing but the daytime temps were probably in the upper 80's, the night time temps maybe lower 70's F.
There's a long story behind it but I've seen a broody hen leave one 5-day-old chick alone all day by itself when the daytime temps were in the upper 70's or low 80's. That chick made it fine.
If you have no adults to worry about integration and you have electricity out there set your heat plate up out there and move then out there. You don't have to wait. To me that is the ideal situation. You don't have to lower the temperature unless you really want to. If you provide one spot warm enough on the coolest temperatures and they have a spot cool enough in your warmest temperatures they will regulate the heat themselves, plus get acclimated to cooler temperatures. In my brooder in the coop I put chicks in that even when it is below freezing. I keep one end toasty warm but the other end may have ice in it. They regulate themselves.