Again that can be very true BUT unless you are dealing with a pure strain, a landrace strain, the strain or strains it is crossed with, even though it might still be sativa dominant, can really shorten the flowering time. If you buy from seedbanks if they do not give you a general flowering time in the seed/strain information ask them because I have made the error before of growing very dominant sativa hybrids and just assumed they would need a longer time to mature and when I first looked at thetrichomes they were already mostly or all brown and I blew the grow. It only happened twice but that is more than enough time and effort and money to waste because you just assume something is very sativa dominant and it will take longer to mature so you dont keep as close of an eye on it around the more common number of weeks for maturing plants.
Get as much information as possible if you can when you pick your strain/hybrid and it will save you from making an error like I have.
I have grown pure sativas that I thought would NEVER mature but just add a little bit of the right indica to the same strain and presto chango that ultra long maturing time can be cut way down even though the plant looks totally or mostly sativa and has a mostly sativa buzz.
That is what really ruined the old 60s and early 70s Mexican that many people either have a hard time believing or refuse to believe was damn good. Later growers started to cross indicas with their sativas and they did not learn fast enough that the maturing time would be so greatly reduced and suddenly what had been really good pot at super low prices turned to crap and the Mexican brick-weed era began where it got the reputation of always having been weak and low potency when if you just went back a number of years what used to come from there could and would knock you on your butt and at the time would cost like $10.00 for a lid, not a weighed ounce but a lid where the baggie was so full you could hardly fold over the flap to close it. You would get higher than a kite and a bag would last forever and it was as cheap as dirt. Then the crosses began to be grown and the landrace strains died out and instead of being as cheap as dirt it was about as potent as dirt and often times that came from it being grown to long because the growers were used to such long maturing times and werent smart enough to figure things out for a good while.
One of the most important things to learn is what each strain/hybrid you grow needs in nutes and how that changes at different stages of their development and maturing time.
Information, knowledge about that is VITAL and every bit as important as anything else when it comes to growing because if you dont know what a particular strain/hybrid needs and its general maturing time and then begin to watch it closely when that time is getting close you are in the dark about things that can make or break your grow regardless of all else you may know.