How to work out difference between H:i times on a 24 hour clock?

Question

I am creating something that calculates fees based on the duration of a nightly event. Sometimes these events go over into the early hours of the following morning.

I have a table in my database that looks similar to this (just so you can see how the dates are formatted):

Start Time        Finish Time
23:30             00:00
21:00             01:30
20:00             22:00

There is no date or timestamp attached to any of these times. It is assumed that if the Finish Time is "earlier" on a 24 hour clock then it must be the day after.

I am lost.

Answer 1

如果结束时间小于开始时间，则将24:00添加到结束时间并进行计算。