If I may add a suggestion based on the Australian system @SimGuruGeorge,
Over here for part time and full time jobs we have a set amount of holiday leave per year, and I think if you don't use it, it can roll over to the next year in some cases, also we have several different types of leave aside from that. We have a yearly allotment of sick leave, and compassionate leave that doesn't roll over, and if you have a child you can apply for maternity or paternity leave.
I think this would be a good idea, having a sim have a certain allotment of leave per the calendar year, 2 weeks minimum but as you level up in your career you can get a day more for your yearly leave per career level? Also the leave for sims with jobs can roll over to the next year and maybe cap out at 6 weeks? And maybe have the children be able to take 2 weeks worth of leave per calendar year?
Alternatively, put an option in the gameplay menu "Do calendar holidays use up vacation days? - Yes/No"
