I've never done but I would graft when you see first sign of growth, ..plant them first.

You can graft your rootstock and then store them for weeks/months in refrigeration. Professional nurseries will often provide a couple weeks of dark storage at warmer temperatures(70F) in order for the graft union to callus over. They then refrigerate the grafts until ready to plant. I've stored bench grafts for over a month in my cellar which stays between 40-50F. Keep them well wrapped in plastic, and the roots in moist sawdust, straw or peat so they don't dry out.

As noted, it is commonly done. However my limited experience is that best results occur when you plant the rootstock and then graft when the root stocks are beginning to break dormancy.

It is more difficult to graft onto planted rootstock especially if you have bad, back, feet, etc. But you quickly get the hang of it.

I bench grafted a quince tree and then kept it in a dorm fridge for at least a couple of weeks.

During that time it formed ice formed on the tree and roots. It established fine.

I did 25 last year, stored them a few weeks. I got concerned about mold,dry etc, so I potted them, and stuck them in my heated ice fishing shack. three snow storms and a hundred pounds of lp gas later they turned out well. with lp gas at 5$ per gallon I'm not going to heat the unless I really have to. I have a ten year old son who hopes to pot 50 of them and sell them in 2 or 3 years. thanks for all the input....it confirmed my thoughts