I know how you feel. The first time I left my son with my sister and mom to go to dinner, and he was two months old... I was on the pay phone at the gas station where we had stopped to tank up. I was on the phone the minute we got to our friend's house. My sister was in tears laughing. Until she had her first child...
I think that your plan is very sound and I think that, at 6 months, your baby will be able to handle a few days without and and Grandma will
having the baby all to herself for a few days. Nothing like snuggling and loving and spoiling a baby then handing them back.
Go, enjoy yourself, miss your little bundle of love, but enjoy the time with your husband. Trust me, moments like those will be few and far between for the next 13 years.