You start paying for the car the day you enter your PIN into the dealers system the day you pick up your car.
My understanding is PIP is paid in arrears so your payment due the 5 days before you pick up your new car will be paid to you in full and the next months payment will go to Motability except the 5 days due to you before you collected the car.
I think I’ve got that right, if not I’m sure someone will be along to correct me.
Have fun in your new car.?