Bob,
Yes 85-90 Fahrenheit. Take a look at Scott’s post in this thread Grafting grapes onto wild rootstock - #3 by scottfsmith. Cooler temperatures are not something grapes take very well. I try and get plastic bags over them in cooler weather to heat them up. I learned grapes don’t root well in cool temps when I tried to root them in ground years ago several times. I rooted some in black plastic pots because of the extra heat. Same with the grafts. Here is another link confirming the 85 degree temp requirement for callus Northern Grapes: Grapevine grafting (part 2): Callusing and rooting.. I’m going to pack a bag with some damp peat moss or paper towell to bump up humidity around the graft.