Please help! would you drive an hour to mind your grandchildren?

Could you stay over so that you can be there for an early start without the hassle of the traffic? When my DD first went back to work I used to drive 75 miles to pick him up from nursery by 4 so that she could stay late at the office. I would do play/bath/bedtime and the next morning she could leave at 7.30 while I was doing breakfast and then I would take him to nursery about 9/9.30 and drive home. It worked very well. but it was only once a week. and I only looked after him for the whole day when he was unwell with chickenpox and couldn't go to nursery.
Does she have a back-up if for any reason you can't do this? I agree that it has to be your decision if you want to do this. I enjoyed getting to know DGS better by having time with him and only stopped when she started maternity leave when she was expecting her second baby.
As to whether it is a natural thing to want to do, well all things being equal, I think it is for most mothers/grannies, but reasons such as distance, ill health other family commitments or age may make it impossible.

could you stay over one night a week to cut down on driving - and the cost of fuel? A friend of mine used to rail to London and stay overnight to look after GD 2 days a week.
I know one person who drove her baby about 40 miles to her mum's house and then back again the same distance for work at 8am, and left baby with nan overnight. So that is another way some people manage it

If you want to do it and it feels natural to you, why not try it out? If it doesn't work, just explain that it doesn't and why – heavy traffic, too exhausting at your age or whatever.