This sounds like what I go through most days. They'll schedule someone and then pull them to go help with truck or something, or they'll wait until the last minute to give me help and then we're rushing to fake!pack everything by goal time. There's nobody doing SFS early morning or evening, and I'm also expected to get OPU most of the time, unless I'm swamped and they'll call for someone else to help. We've had high volume lately, and the orders have been coming in as fast as we pick them, but every day it's like it's a huge surprise to leadership that one or two people can't get ahead of it.
I usually stay a little late if I'm nearly done with the packing, but I'm usually scheduled for 40 hours every week so I can't consistently stay late without having lots of time to cut at the end of the week.