@jackstack
Grandma currently babysits 4 out of 5 days of the week, is late 50's, lives 20 mins away and has a spare room set up with cot.
That is an amazing resource. If both you and your spouse have a good relationship with that grandparent and don't mind being around them, then absolutely take advantage of that time to do
anything but caring for your kid.
That's talking 24 hours to sleep, put away laundry, get an oil change, bang it out, clean up the house, get groceries, mow/kill the lawn, have a hard talk, bang some more, mix a few drinks, and/or deploy the toxic-but-effective stain removers.
We have a similar arrangement, with grandma's work a few blocks away - we have always gotten along well, and she will bend over backwards for her grandchild. She's learned how to do the food pump, mix formulas, and she's another source of interactive learning to help baby's brain blossom. She's even watched her a few days over the weekend.
Now, grandpa - not so much. Don't like him, don't trust him to follow directions, don't wanna be around him - the same arrangement would never work, even with the same level of convenience.
But as a compromise approach, I'd say work up to it. Start by spending a night there with baby now and then just to feel it out. And remember, you're only 20 minutes away if you need to dart out the door in the middle of the night.