Don't rely on pro-brewers mash times unless you fully understand their process. Many brewers mash for a time, then recirculate for a time, then sparge for a time, and they are still getting conversion.
Time and Temp determine a mash profile. Both are important.
You should start with what works for you, and then make alterations to suit changes that you want to make.
That said, "Conversion" from starch to sugar occurs quickly, but that is not the only changes that occur.
Long chain, non-fermentable, sugars are reduced to more fermentable sugars. Both time and temp affect this process.