Not too early if they really need to go out, but do they? If they have room in their coop to hang out inside, why not just leave them in? I'm home most of the day and on really cold days, I just leave the door shut because they don't enjoy going outside anyway.
If they are used to going out anyway,don't mind the cold too much, and they do go out even in the winter, sure, open it up! My only worry would be that night time predators are still out and about that early in the winter since the days are so short and it's still dark then. Do they have a pen or do they free range? In the end, it's your call really, chickens do well enough in the cold usually but if there's room in the coop, that may be better for a bit.