A month? Ha! I would keep them separated but able to see each other via some kind of separate cage for about a week, and then integrate them. Depends on the individual birds' temperaments though. I've always been pretty cavalier about introducing new birds immediately and they've always done fine. However there's also enough land here that they can give each other space until they get comfy with each other.
I've found that a lot of the common wisdom about keeping chickens is overblown like that, especially when it comes to roosters. It's not like Highlander where they fight it out to the death. Mine have all grown up together and done fine, but even when a new one has been introduced, they just fight a little to establish dominance and the status quo and it's settled from there.