this might be a "rules are different all over" kinda thing, but im my building its like this. a certain amount of option days must be made available by management every working calendar day of the year depending on amount of staffing. im not sure of the ratio. you then inform your supervisor at least 7 days in advance verbally and in some cases/places with a written request of the day you need/want. if the day is available meaning no one else asked for it yet with more seniority than you, then they must honor your request and give you the day off. you can get bumped by a higher seniority employee if they ask before the 7 days but not after and you can bump lower seniority guys using the same rules. you can also request the day with less than 7 days notice but it is then up to your management whether to honor it or not.