Meeting tenants at 11pm? Concerned about safety. Advice please.

[Maggie Mahoney]

We have difficult tenants in one of our rental houses in Utah. We are not extending  the lease for them and they've been very angry about it. When I asked them when they'll give us the keys, they said they'll meet us at the property at 11pm on Saturday, the last day of the lease. 

We're concerned about our safety but we are also anxious to get the keys from them and change locks ASAP. We are worried they'll destroy the house.

We can't find any law where it says if the tenants have until midnight or end of business day to return the keys.

What shall we do?