By the way, the mobility issue in that particular context seems to be something of a red herring.

The mobility issue would affect doing of the 8 hour walk itself, but unless it's much more restricted mobility than I think you were talking about, it wouldn't affect getting to the bus stop at the start point. That could still be achieved by public transport, but the 8 hour walk still couldn't be achieved even if you drove a car to the start point. Hope that makes sense (it does in my head).