It's actually way more complecated than that. Based on the assumption of indica/sativa ratios, 100% or dominant sativas take longer to mature, but the genetic age of the plant makes the desired harvest time to be based on the color of the trichomes. With sativas you are looking for a clear to milky white. This will retain the up, cerebral, giddy, etc., characteristics of sativas. Indicas mature faster, but in terms of genetic age, you harvest them much later. You'll want to wait til the majority of the trichomes heads have began to turn amber. This is actually the THC degrading into cannabinol. That's not necessarily to say it's bad, if it's correctly timed. The later age of the trichomes on the plant preserve the stony, body, zombie, etc. characteristics of indicas. If you let it grow too long, and you can tell when all or most of the trichomes have turned mostly amber, the cannabinol does replace a large amount of the THC and can result in more of a sleep aid knock you out kind of stone, but it would also be much less potent. Hope that helps.