Silly Car rental ?
 

We are due to arrive at MCO at 22:37 of the 22/12, being that we are on an indirect flight from Chicago. Past experienced have proved that there is always a delay, would you book your car for the 00:00 of the 23, or too much of a risk booking if for the 22 and just lose a day.

I don't think it matters what time you book it, as far as I can remember your rental time starts as soon as you collect the car and you return it before or on that time the day you fly home.

Rental day is 24 hours and starts from time of collection. Providing you return the vehicle by that time on your last day, there would be nothing extra to pay. Only makes a difference if you were to enter a new rental day, not a 'normal' day i.e past midnight. I'd say an hour from landing. Doesn't matter if you're late or early.