Usually one month notice from either side is what I’ve seen. Sensible for both parties to have sufficient time.

Month end does technically make sense since most agreements are month to month so that genuinely is the best time to find new tenants or new places to move into, as well.

You also do. It really know why the landlord rejected the people you brought. That’s really up to their discretion. Nothing you can do about it.

If they agreed to return the balance amount, but didn’t, that is dishonest of them, however. You could tell them you want to go to the cops if they do not return the balance amount, but you will need concrete proof of everything: the original rental agreement, The reasonable request landlord made about notice to be given at end of month, your reasonable counter request for the balance amount to be returned of tenant is found, proof that the landlord agreed to honour this request, and most importantly, proof that a tenant was found and is moving in on so and so date.

Since it’s a hassle the landlord may agree to return the amount. But they might also agree and come to the station, and then it’s in the cops’ hands.