We have 22 pilots, four planes. 15 vacation after 5 years and 20 days afte 10, so there's a lot of vacation to be taken. The guidance first come, but usually can be approved the month prior. If th schedule is covered even later notice. We also get 7 scheduled days off per month and 5 "flex" holidays. The scheduled "days off" are put on each weekend of a week's vacation, due to th fact policy a week's vacation is 5 normal working days for the thousands of company employees. So, 5 days vacation is effectively 12 days off the schedule.
A lot of other things are handled by deft scheduling, not charges to vacation. MiL died, they just took me off the sked for the time I needed. I was next out about 2 weeks afterwards, with a couple of office days in between. It's all about give and take.
GF