we certainly do have plenty of possums and bandits about but our place is very secure but thats not saying you may not have valid point. I may put a game cam out and see
If there are windows that they can see out of, and you have the yard / coop / house area lit up like daylight, he will see everything that goes on. Could be mice, rats, weasels, raccoons, coyotes (I don't know if you're urban or rural but they are everywhere), fox, possum, neighborhood or feral cats, etc...Being a young rooster he is learning to differentiate threats and will be prone to err on the cautious side.
But I doubt the crowing is stressing your hens. However - have you had cameras in there and see a change in behavior at night, compared to before this fellow came along? I think your Buff O.'s will accept his behavior as normal and won't be stressed out by his crowing. Often a crow is an "all clear" signal, so it's a reassuring sound to them instinctively. Is he giving a warning / alerting sound prior to that and getting everyone on alert? That would "wake" them up fully if so.
[You may know already, so forgive me: chickens are up and down in the night usually. Sleeping, preening, hanging out, etc, dozing again. They will sleep with half their brain and stay "available" with the other half. They do sleep with all their brain too at times but it's not the whole night.]
I am quite a bit north of you but here too everyone goes to roost about 4-4:30, even the experienced hens. It's wintertime here in Central New York with the sun low in the sky and still short days.
Of 3 two-year-old Buff Orps only one has started up laying again, and that was only about ten days ago. Of the other two hens, one is getting a reddish comb and one is still very pale. My Buckeye 5+1/2-year-old lady I don't expect to be laying much at all, she's a garden manure provider now, but she might have a Spring Flush and lay one or two, which hasn't happened yet. None of my four Buckeye pullets, hatched late July /early August, have begun laying either, though Buckeyes are a late-laying breed.