depending where your tree is and how far along, you can try to increase the survival odds by minimizing drying…I’m fairly convinced that if you had a “perfect” humidity control you could graft a fully leafed scion, the biggest problem is drying…
so you can try to wrap the entire thing in parafilm, put a plastic bag on the branch, take it indoors/to the northern side of the house, and/or pinch most leaves off to minimize the scionwood dry-out before the graft takes…I was babying some tiny pawpaw by leaving an inverted glass jar over it for 2 weeks as a greenhouse, taking it off every couple evenings for 4-5 hours to avoid things getting wet enough to mold…