Sometimes when I open the pop door for the first time all chicks are on the ground within 15 minutes. Sometimes it takes three days for the last one to decide it's time to brave going outside. I don't get stressed about it and don't see any reason to stress them. I let them work it out on their own terms. They will.
I often keep mine in the grow-out coop section only for a week or more before I let them in the run. They almost never go into the coop at night on their own. I think that has to do with mine being elevated. My brooder-raised chicks typically don't start to roost at night until they are around 10 to 12 weeks old. I've had some start earlier, some start later, but 10 to 12 is a good average. Until mine start sleeping on the roosts they sleep in a group down low. That's why i think mine being elevated has something to do with it, they sleep on the ground, not the coop floor. I don't have that problem when the coop or shelter is at ground level. So every night after dark and they have settled down so they are easy to catch I lock them in the coop. Eventually they will get the message and start putting themselves to bed in the coop when it gets dark. I had one group that I only had to do it once, some take three weeks before the last ones get the message. My groups are often in the range of 20 chicks.
I don't know how old yours are, what you coop and run look like, any of those details. More info and photos might help us spot something significant. Since I do not consider my run predator proof I am willing to stress them to lock them up safe in that coop at night.
