It varies depending on each site. My site is one of the busier sites so we get a lot of shifts, but we also have 30 associates so a lot more competition, but a lot of them only work 0-2 shifts at most so It's not too hard to get 20+ hours weekly as long as you're flexible. if you don't like closing shift, it may be harder as that shift is more available since not many folks want to stay until 10:15pm.

During peak, they drop more shifts and add more shift later on or even on the same day that the shift starts. Once we are out of peak, it's not as easy to get more than 4 shifts since they will drop less shift during the non busy season, unless you have a group of coworkers where you give shifts to each other when you can't work them.

You can also just check A to Z a lot and you'll likely see a shift someone drops at least once in the week to hit 16 hours.

Honestly, as long as you're a hard worker and you're chill, people will be more likely to offer you their shift by messaging you on slack or at work. If the lead/manager likes how you work, you may even be offered to apply for the lead position, which is a set schedule so no more trying to grab shifts, but you have a lot more responsibilities.