Flowering Outdoors Question

I know that during flowering both indoors and out, the light needed is a 12/12 schedule (12 hours of light followed by 12 hours of darkness). My concern is how this works outdoors.

Most people that I've asked suggest that if you've planted in early May (11th for me), that I should harvest sometime in October, as flowering should begin sometime in September and conclude in October.

I've looked up the sunrise and sunset schedules of my region, and here is what I've found in terms of dates and their respective light schedules:

-Sept 1st-18th is around 13/11
-Sept 19th-30th is around 12/12
-Oct 1st-4th is around 12/12
-Oct 5th-31st is around 11/13

Now my question is this - do these hours (and sometimes minutes) of change regarding light/darkness affect outdoor flowering?

Thanks!