When the tree installs its roots, it sneaks into the ground like you do in your bed under the blankets. So, the soil'level rises as much as the volume of wood contained in the stump and the roots. Actually a little less, as there's some compression of the dirt between the main roots. That is, for a tree naturally grown in place from a seed. If it was planted or it had some ground work around it, this blurs seriously the picture.
When the tree disappears and the fungi digest the wood, the soil comes back to its initial level. That can take quite a long time though.
I've done some 5' stumps with my baby grinder, not in 35 minutes but more around 1.5 day.
Most of the time, first, I remove the obvious part of the cone of dirt with a pickaxe to make my reference level. I shovel this dirt aside.
Then, I grind the stump flush to the said level. The chips are mostly wood and easily removed.
I take again the pickaxe to dig the dirt around the stump and main roots to about 6-8" deep by the same in width, dirt shoveled aside. This gives more "clean" dirt, gives some room to put lower the guards and bearing of the (small) grinding wheel and the teeth see less dirt/sand/gravel (the lifetime of the edges is noticeably enhanced).
Stump grinder again, this time, nose down to the final level, around 8-10" deep. The deepest I went was about 16". Batch by batch, I shovel aside the debris, trying to sort what is mainly wood and what is mainly dirt. For the big stumps, I fill back part of the hole with the "mainly dirt" and dirt to push and operate my stump grinder over it.
At the end, I finish to fill back the hole with the remnant of the dirt's pile. Usually, I come pretty close of the general ground level.

That takes time and it"s labor intensive, but I'm pleased with the result. I have less weight to evacuate (fewer dirt in the chips) and usually no dirt to bring back.