With that time constraint in place, we decided to take the 10 AM train rather than that 8 AM train out of Centerville, even though that means we won't get up to my mother's place until later in the afternoon. If it weren't for the 24-hour limit on the car, we probably would have aimed for the earlier train this morning and a later train coming back, for a roughly 30-hour cycle, but it's not worth another $40 for six more hours of car rental.
It's still a relatively quiet Labor Day Weekend, something I'm not at all used to. But given my eye and balance problems, I'm just as happy to not be in the middle of a Worldcon right now.
Edit, 8:45: Modified to include the specific reduction in driving. In case it isn't obvious, I'm very grateful for Cheryl's help here, and I've also wanted to try out this train-rental car thing anyway, so this is a good opportunity on a weekend when, for a change, we are not under a whole lot of pressure.