My girls head in before it gets too dark, but considerably darker than the lit coop.
How old are your girls? They wouldn't go in automatically at first, especially since my ramp is fairly steep due to the coop being raised. I lure them up with some of their favorite treats, and others will follow. I had one that couldn't figure out how to get up but knew she was all alone, I had to lead her (like with training dogs) by holding a treat right in front of her and lead her up on the ramp.
I do that a few times if they are still around outside when it's dark until they figure it out. Now it's automatic. It also makes the short days more noticeable as they have been going in earlier each night. Right now it's about 6-6:30. Summer is about 8:30-9pm
Do they free range all day, every day? Or just for a short time at the end of the day? I've noticed that when mine are out all day, they go in earlier. If they had to be confined most of the day for some reason, they stay outside much later, trying to make up for lost time.
The coop is lighted with LEDs and the 26 girls free roam a 1600 sqft fenced field. They are just 5 months and we are getting 5 eggs per day. In the summer they were in at dusk but now they stay out till fairly dark.
I noticed the girls sliding down the ramp between the cleats so I covered the ramp with a tire tread. They are readly available on the side of most highways.
The first day they came out and didn't go in all day while they checked it out. Now they walk up and down and don't slide at all.
I wrapped hardware cloth around one of my long ramps, stapled it to the underside. That gave 'em a grip with their feet.
MOST of my chickens are in well before dark, even when it's kinda light in the dusk. But the youngsters - like any kids, I guess! - stay out longer. I think they enjoy the chance to wander close to the coops without all those SENIOR hens bossing them around. Grab a late night nibble at the feeders, check for bugs, etc.
And yes, the rooster calls to them from inside the coop after he has rounded up all the older ladies.
It sounds like ur doing everything right . They just haven't reset their internal time clocks to go with the sun yet. I get out betiween dusk & dark to let mine in and if I get out too early while there's still a little light they take their time. If it's already dark, they run for the coop & go straight in.