Varying Lighting times based on global charts

I am trying to do research as to what the perfect cycles are for time based on the genetics I'm growing and every light chart I can shows a max of 16.5 hrs of light during peak season times. I grow indoors, is the 18/6 or 20/4 pattern better for the plant even though the natural light cycle is much shorter? I'm guessing it just allows for more growth during the longer light cycle, but is it necessarily better for the plant? And will a shorter light cycle like just take the plant longer to mature? Look forward to the input. 8-)
 
Top