Attorney wants a paralegal to be present on rotation for Saturday hours 1-2 a month. I refuse to be a part of the rotation

I made a post about my firm last year. This will be an update to my previous post. Our office opens 1-2 Saturdays a month from 10am-2pm so the attorney can handle consultations or start cases for clients. Her reason for being open is to bring in more revenue and it allows our clients who aren't available during the work week to come in on the Saturdays our office is open. One paralegal is required to be there to do client intake, handle calls, and work on the new cases as the attorney meets with prospective clients. Our boss wants to rotate this responsibility among the six of us.

I value my work-life balance and don’t want to spend my Saturdays at work, especially since the commute adds about 80 minutes total roundtrip. I draw a hard distinction between work-life balance and I desperately need my weekends to be free so I can decompress. The overtime pay isn't enticing to me. I’ve managed to avoid it for nearly two years by being unavailable or letting others volunteer, but I want to make it clear I’m not an option for this rotation.

It seems like a coworker complained about how not enough people want to volunteer (but like who tf wants to come in on the weekend lol) to come in on Saturdays during their annual review because my boss mentioned how she wants more of a rotation in a recent meeting where we discussed input from our team about how we can manage things better with the firm. I feel like I'm now in a position where I will be pressed to come in, even though the employee contract I signed when I joined the firm didn't mention having to come in on the weekends. It also wasn't listed on the job listing I applied to or brought up during my interview.

I plan on leaving this firm this year. In the meantime how can I politely but firmly refuse without causing tension? I have a feeling my coworkers might pry if I say I have other obligations to fulfill that make me unavailable on weekends.