The hours are one of the benefits, but one of the drawbacks as well. It is a hard adjustment for some people to get up at 3:00 AM to go to work. Also, starting pay is not that great. Oftentimes, preloaders that you supervise who have worked at UPS for several years will be making more than you.
If you take a part-time management position with the hopes of getting promoted to full-time, well, good luck. UPS has always treated me well, but from the day I started I have been told that there are promotional opportunities. If you take the job for extra work, then that's great. If you want to make UPS a career, then seek out the positions that are full-time and apply for them directly. They need part-timers to run the day to day operations, so some managers don't really want to help people develop a career with UPS because then they would have to find someone to replace you.