12/12 is a sure-fire way to make sure your plants flower which is why it is recommended. The fall sun DOES NOT equal 12/12. the amount of day light changes every day. every, every, every day getting a little longer/shorter depending on the season.
it is normally recommended you stick with the circadian rhythm (whatever light cycle you use it should add up to 24 hours) but i have not experimented with any other light cycle during flowering and would be very interested in reading about quality experimentation (control group and double-blind would rule but just trying something other than 12/12 and reporting on it would be cool too!).