If a plant gets pollinated at week 3 of flower, which is about minimum time to mature enough for best results, then the flower time is about the same or maybe even shorter in a sativa. My sativa got pollinated mistakenly last year and it finished sort of early I thought, for a sativa. Not 100% sure on the sativa though. Some may still take 16 weeks to make seeds, too. My observations are on mostly hybrids. If a plant gets pollinated late in flower I think the flower still dies off almost at the same time and maybe with seeds that don’t mature.
It’s a good question to try and understand the details in the timing. Some strains may perform different, I don’t know.