For reasons probably shrouded in the mists of time, car insurers tend to finish the policies one minute before midnight. Let's say the policy says:
If you enter it on the system as 19/12/2025 then Plait assumes you mean 19/12/2025 00:00 (since the field does not allow the time to be specified). You should add one minute to the stated expiry, and enter 20/12/2025.
Open question: What happens if this person has a car crash at 19/12/2025 23:59:30? Are they really not covered by their insurance? If anyone knows please tell us ;)