I was careful describing this process, but it shouldn't overshadow the fact that it doesn't take that long if the issue being fixed is favorable.
The worst factory plane I've had to correct, well, two - one stanley with twist and low toe and heel (concave), out about 7-8 thousandths of an inch. bad!!
The second was the norris A13 that I posted about not long ago - it also had some twist but it was bellied convex instead of concave. I think the issue with it was wear - it no longer had its original iron, either. It's possible that it moved some. I draw filed the center out of that plane and then lapped it, leaving the very toe and heel just a tiny bit proud (good enough).
Both of those worst cases were no more than two hours (with experience, they were closer to an hour, and on big planes).
For most small jobs like this one, the process is quick, though, and is as much about the work that's not done as it is about the work that is done. It's a lot like sharpening a plane iron - directed pressure on hey spot never gets out of control. Messing up and rolling up the back of an iron accidentally and rounding the edge (or flattening an iron on stone concave in its length) can become a real case of chasing errors with other errors. We're avoiding that.