I wouldn’t have a hard or fast answer, and it also depends on the stage. If you asked what it takes to get to a final CAD database for a car in the industry the answer is probably on the order of magnitudes of months->years.
If you were trying to build your first model out (not including the entire clay workflow or detailed design), I could see getting to a fairly clean initial model in 2 weeks. Would probably depend a lot more on the design itself. My old boss told the story of modeling an entire truck cab in a mad blitz weekend contract, but that was years ago and with different surfacing expectations than today.
A huge amount of the work that professional CAD sculptors have to put in is in the back and forth between clay & CAD. So doing the surfacing is one piece, doing mesh cleanup and back and forth with designers is another story.
It also will vary based on your expectations of the surfaces. There are techniques that will get you surfaces that are not truly Class A but would still look great for a model, concept or render. If you want to explore form that’s completely adequate, vs production ready 7 degree 1 span surfaces.