While I think that the question is interesting, I agree with xiota on the opinion/personal-part and the definition of look-part, but I think it is a problem of broadness, too:
A press photographer will spend a few seconds at worst (less time = better), while I know people that spent a whole summer - even a year - for a single project.
Are we talking press? Landscape? Portraits? Studio? Outdoor? Money-style professional? Ars-artis-gratia-style professional? Serious hobbyist? Instagram? Holiday with family?
I would/will spend different times on look development in each of them. And not even then can I answer it straight away: I had projects that were done within hours and I had projects of the same category that took days.
While empirically, there might be some correlations, we have (AFAIK) no study for that, so all we can offer is our own opinion. I would gladly share and compare mine with others, but I fear that's something beyond the scope of StackExchange.