Chickens do NOT like new comers, at all. To be honest, the whole "put them in at night" thing has never worked for me, ever. It's a real good way for your new bird/birds to get the heck beat out of them in the morning. I had a hen scalped and nearly killed trying that. The older hens know full well there is a new bird in their midst. It might work if you have a very large flock. Smaller flocks know who's who.
What has worked extremely well for me is putting new birds in a separate pen alongside the older ones. Or fencing off part of the run for them. Let them get used to seeing each other around all day, every day for a few weeks. It's well worth the effort. I raise my young birds in a grow out pen right alongside the older hens. I don't let youngsters mix with older birds until they are about the same size and can defend themselves better, about 15 weeks old. By the time I do let everybody out together I have almost no pecking at all, just very minor pecking order issues. No feather's flying and certainly no blood shed. Chickens can be brutal and once they get it in their heads to attack and peck a new bird, they don't always get over it. Been there, done that too. Give them the time they need and there will be a lot less stress for both them and you.