I'm in the same boat. When I ask, the answer I got seemed to depend on the rootstock. In my case, I'm grafting seedlings so each rootstock is unique, not clonal. So far, none of mine show signs of starting growth. Things may be different if one is budding established trees. Mine are small seedlings started last winter and still in containers. I'm kind of glad they are not leafing out yet. I don't think there is enough time in my area for them to put on enough growth to harden properly before they go dormant.
I plan to let mine continue to grow normally and produce as much of a root system as possible this year. When they go dormant, I plan to cut them off just above the buds and put them in my cold room to overwinter. I'll probably wake them up early and put them under lights. Those that take, I'll transplant into larger RB2s for the next growing season. Those that don't will probably get culled.
Thanks,
Jack