Regarding the calculation of leave time

First of all, let’s talk about the rules for asking for leave:
1. If you ask for leave in the morning, the duration shall not be less than 3 hours
2. If you ask for leave in the afternoon, the duration shall not be less than 5 hours
3. Working hours: 9:00~18:00
4. There is one day at noon Hours of non-working time
Because of the company's system, overtime work is not paid but can be compensated, so the time must be accurate to the hour. Then the question comes:
1. If the time span of my request for leave is from morning to afternoon, it meets the rules, but the system calculation time will be one hour longer:

• My solution is: first determine whether the start and festival time are on the same day, then determine whether the start time is in the morning and whether the end time is in the afternoon. If both are satisfied, then subtract one hour from the time calculated by the system

2. If some people are stupid and choose the start and end time beyond working hours, for example, the end time is after 18:00, then they have to judge whether to deduct the time after 18:00

3. The most troublesome thing is if the holiday includes legal holidays, weekends and other special circumstances. There are also non-integer numbers that span days. For example, if you only ask for 11 a.m. three days later, how do you delete the period from 0:00 to 9:00 three days later

My thoughts are a bit confusing, so I would like to ask experienced seniors to share their experiences, thank you! !