Monday is Memorial Day, and a closed receiver is not a delivery.
If the warehouse is shut, do not roll a truck up to the gate and then argue about detention. Detention is for a dock that is open and will not take the freight. A holiday is a closed building.
Move the appointment
Deliver Friday or Tuesday. Put the day on the rate confirmation now. If the freight will not hold until Tuesday, the shipper needs to say so today, while you can still find a receiver who is working.
A driver who spends Monday night at a locked gate is not late. The appointment was wrong.