Here's our experience:
Took almost 12 years for hubby to get a full time position; he went from part time to full time, but in his case, it was a crummy listing that was essentially 2 part time positions that equaled full time; He worked as an air driver Mon-Fri 4:30-8:30 p.m., then Mon-Thurs he also worked in the hub sorting. He loved the driving part, hated sorting.
He was fortunate in that he went from PT to FT at the same time as moving to air driver, which helped him take the next step to full time cover (called "swing" in some hubs) driver. Going from air to cover took 2.5 years. Cover driver puts you one step closer to getting your own bid route, and was a little rocky last year. Being low man on the totem pole meant he got sent home many days. Three drivers retired in December, so I think he'll be working more solid hours this year. He's been doing this almost a year now, and there are maybe 5 guys below him now.
It IS very different from the corporate office i work in, so it took a while to wrap my head around it. It's definitely worth it in the end, but god they make you play the loooooong game to get there. The driver for our office said he heard it is a 19 year wait now from new UPS hire to full time bid route driver in our hub, and that sounds about right. Hoping he gets his own bid route in the next 2 years.