So here is the rough list of things that happen.
1. Get LaVerne seedling in pot
2. Plant it in the ground
3. Let it grow new roots
4. Let it grow new leaves
5. Top the trunk at some height: knee, waist, or chest.
6. Let it grow new branches
7. Graft onto the end of new branches
Zarafet, if I understand you correctly, you're asking about grafting it after step 1 versus grafting it in step 7.
I don't think it's a good idea to graft in the pot. The plant is not as strong as it would be in the ground.
The stronger the rootstock, the more vigorous the graft. I think doing it after step 5 is stronger than step 7 since the full strength of the tree is on one graft rather than divided among several branches. How do you know the tree is strong before it grows new branches is the problem with trying to do it earlier. It'll grow more roots the longer you wait.
If you get a tree now, there's not much time left to graft this year. So you need to decide to graft it in before October or next April-May.
Anyway, definitely put it in the ground first if that's the ultimate goal for it.