As long as you have 3-4 days of temperature above 65 and no freezing, you can graft persimmons. I found the best time is when buds start swelling and the weather god gives you a 3-4 days of >65 degree. The earlier the better.
So you are more than OK to graft now. Remember to remove the new shoots from rootstocks (remove most now and remove all when the grafts take).
See this video of how Chinese orchard farmers bud graft persimmons. The rootstocks were most likely lotus. Note the peach tree blossoms in the background and the buds on rootstocks were still tiny.
Cut off the side branches and W&T at the height you want. Diameter looks good and it should grow well for you. Diameter doesn’t have to match perfectly although it can if you have wood the same size. Just ensure perfect alignment on one side and you will be golden.
HOW TO MAKE YOUR SCION MATCH: Cut the scion for a cleft graft. Cut your tree. Lay the scion across the top where it stretches from side to side. Note location and make cut there. Now it’s a perfect cleft on both sides. I love cleft grafts. Much sturdier than bark grafts.
The biggest reason I don’t whip and tongue or cleft graft the end of the branch / whip when topworking persimmons has nothing to do with the grafts taking. On well established seedlings, your scion can easily push 6 ft. of growth. Also the leaves on newly topworked trees are massive. Between thunderstorms, temperature swings and fronts moving through, we get a fair bit of wind here, I have to spend a lot of time securing the new growth and/or pruning it back so that it doesn’t snap right off at the graft.
My method now, similar to what I do with mulberries, is to side graft partway up, leaving the rest of the trunk. It makes a nice stake. , The nurse leaves I keep help the scion to push too, I believe. I’ve observed scions at the top of stems just sitting there, while the rootstock has decided instead to put its energies into pushing buds down low. My method keeps the sap flowing past the graft until it’s made connection. Another nice thing is that you can also put as many scions on a rootstock as you care too. I often do 2 single bud (scion, not t or chip) grafts instead of a single scion with 2 buds, as I might do with apples. That way, I figure I have double the odds.
I probably have around to 90% take, though I was more like 25% my first couple of years.
I just looked today, one of these trees went from 3’ tall and 1/4” caliper at the graft to 10’ tall and 5/8” at the graft. That tree, a JT-02, had a second stem slightly smaller (the 2nd graft) that DID snap off despite my efforts to lash it off. I was outside that night fortifying my stakes and Velcro ties for fear I’d lose much more
I think your choices are many, temps are about right and a good time with buds breaking out! I would tend to do whip & tongue at a height matching scion diameter and a chip bud just below that as an insurance backup. Rootstock seems healthy so even if you fail you have plenty time to graft again. Another if you want to graft lower would bravado z graft where your size does not matter as much, but I fave the whip & Tongue as a stronger graft union than Z! Good luck Trev. I am just starting outdoor figs using Z grafts and bark grafts to top work a mature tree to earlier varieties.