If your T has offered Saturday sessions it's because s/he is ok working on a Saturday - let them worry about their schedule. Not sure about the "just sitting there" thing tbh, I'm nearing the end of my training to be a T and honestly, it's hard work to really listen to and engage with your client. Not hard in the way digging ditches is, but physically and emotionally draining. I'm not complaining at all, just saying that a T working properly is doing much more than just sitting there.