Personal days, optional days...they are scheduled by MUTUAL AGREEMENT. Your supervisor has to give you an answer seven days prior to the day you request. Therefore, you were correct to ask for it when you did, so that staffing can be checked and an answer given. Too many people ask with only seven days to go, well, that will be denied every time. You need to understand, based on staffing for the day you request, and taking into consideration anyone else requesting a day off for the same date (seniority rules, you know), the answer may be no. I hope you get the next day of your choice. Good luck.
Oh, by the way, UPS does NOT schedule your vacations, they are chosen, by seniority order, by the bargaining unit.