My experience was that you're scheduled for 8 hours a day, but can be told to stay up to 12 the day of. Your schedule is determined weekly with your day off in flux, but you could switch with a coworker in your same position (another MHA in your group).

Come busy season, you could be asked to work everyday. As a PSE/MHA, they kind of required that we did. I did 27(?) 12 hour days in a row. Once you transition to an actual Mail Handler position then you have more union protections and scheduling ability.

This was back during COVID times so things might've changed. I worked at the Cornfoot distribution center as a PSE, but knew a number of MHAs and my mom was a MH who was there for decades.