Are you certain that these are international concepts? I've seen it broken down in even finer detail: vacation, national holidays, personal choice holidays, and sick time - all of this referred to collectively as "paid time off." There were internal rules about each one was to be handled, but I was never confident that these rules were the same from company to company let alone from culture to culture.
What is it specifically you're trying to say and in what context. Here's an off the cuff example.
- I have used up my sick time and will have to use vacation.
- Mi elĉerpis mian forpermeson pro malsano kaj mi devos uzi feri-horojn.
I suspect that "overtime" (especially in the sense "more than 40 hours) is an American concept - but pluslaboro does seem to be a calque of German "Mehrarbeit" which is similar. (Not sure how that relates to "Überstunden".)
Another option is kromlaboro which is what Google Translate gives and is found in Tatoeba. Your suggestion of kromaj horoj looks similar to the French expression "Heures supplémentaires"