If using midnight as part of an 'End Time' the 'End Date' will also need to change, since it would be the next day.
In the below example. I've attempted to change the end date to 12:00am on October 2nd, but the Booking start date of 8:00pm October 2nd.
The end date & time cannot be before the start date & time therefore the update will not save. I will need to change the end date to October 3rd to allow the end time to be 12:00am
Additional Information
If you do not wish to have a different 'End Date' you can change the 'end time' to 11:59pm