Since we are getting into the finer details of a Dry Martini here, another question is; what is the optimal stirring time?

I prefer Tanqueray No.Ten gin with Cinzano 1757 Extra Dry Vermouth:
https://www.tanqueray.com/en-us/recipes/tanqueray-no-ten-gin-martini#method

Also, if stirring 2 drinks instead of one, does the stirring time need to be doubled in order to get the same amount of dilution and chilling?