In a game I played, the Bandit Archers took their turn. Later in the same round, we opened a door and spawned Bandit Archers in the new room. Do the new Archers have a turn this round, since the other ones already had their turn?
Yes and just after the end of your turn.
Besides, you don't flip another monster card for them. Even if you've cleaned all Bandit archers in this round before opening the room.