"Extrome" said it - "It's in the genetic's" . 18/6 in normal time for auto's (some say 20/4) But use this time thru grow but switch to flower lighting and still use 18/6 at week 3 or 4 of auto growth:
Auto growth cycle:Germination/Seedling stage - 1 week
Vegation stage - weeks 2-3
Pre-flower stage - week 4
Flower stage - weeks 5-8 ( some auto may finish in 7-8 weeks while other will take up to 10 weeks of flower