Gosh, you are all so kind! As the grandma, I would be looking forward to a little break until you went back to work, while still offering the occasional afternoon or morning childcare. I wonder what happens the other three weekdays, is your little one in nursery? Or maybe you only work two days. If you want to keep the routine, I would have thought either keep to the mornings or the afternoons; that way it frees up a whole afternoon or morning for the gps. Also maybe they would like to go away on a holiday!
I do think today's families are so fortunate in that grandparents are willing to help with childcare. I had three children, no help whatsoever. No, I didn't go out to work, but then I believe caring for ones family and home are actually a very valuable work to both the family and our society. ( and no, we didn't have loads of money - just went without what seems to be regarded as necessities today).
Moany hat off now ………. as others have said, best thing is for a good discussion by all on what each party would actually like and enjoy!