I've been trying to think why you'd ask this. What are you trying to control or what do you gain by when you open the pop door? Is it just that you've read the pop door should be open at sunrise and you don't know why? I suspect that would cover a lot of people on here on a lot of topics. That may be why they are on the forum.Just wondering how others time their chicken release.
My definition of "sunrise" in this is when can they see well enough to start interacting, eating, and drinking. I don't see official sunrise having any real bearing on it. That can be quite a bit later on a dark rainy morning as compared to clear skies. So it can vary, let alone with the daily variance on official sunrise as the season progresses.
Predators aren't one of my concerns as much as it is on other people's minds. Mine are released into a pretty predator resistant run and a large area protected by electric netting. If predators became an issue my attitude could certainly change.
I feed and water both in the coop and the run. If you only have food and/or water outside you might want them to have access to it sooner rather than later.
My coop is big enough that I don't have behavior problems if they are left locked in the coop for quite a bit of time after they can see. If your chickens start beating up on each other if they are left locked in the coop for any length of time you have an incentive to open the pop door pretty early.
Your life schedule has an influence. If you have to leave for work at 6:30 every morning that may set your timing.
Like Aart, I'm retired. While my wife won't let me be a hermit I can see some real benefits to that lifestyle. After rereading Aart's post I can see a lot of similarities in our thought processes on this topic. I generally don't go down there to open the pop door until after breakfast which often means 9:00 AM or so. If something special is going on, like when I integrate, I may be down there about the time they can see to interact.