It will start from wherever the tool is. Once you set the machine work origin, the gcode essentially locates there. After, you can move your spindle wherever and it will move to the first cut.
The origin is the datum for the stock location, not the tool location. The arduino (or whatever controller) will take care of the rest.
So, in fusion, you won’t be able to simulate any beginning moves, because you 1) can’t tell it where the tool starts and 2) can start from pretty much anywhere.
It’s been a while since i used ncviewer, but i bet the move from 0,0,0 is also just an assumption, and that you can’t change THAT either, without manually inserting another cut/travel move first. Of course, fusion simulation uses the toolpath BEFORE posting, so you can’t even try that if you want to. I think. One of the recent updates saves a copy of the gcode in the manufacturing tree, so maybe you can edit it, but I’m still pretty sure there is no way to use that for simulation.
I think you’ll save yourself a lot of headaches if you just remember that you can leave the spindle wherever you want and it will travel to the first location in the gcode.
Is there some particular challenge you’re facing with sending the spindle to wherever you want it before running the program?