Your wrong because that is just a estimate given by the seed seller. Lights, nutes, enviornments then the trichs. The seed sellers tell you this cause that's the length of time it took them to grow seed to harvest i believe it's what their trying to sell you. I still just wait for the plant to give up and show it's amber or how it looks. My 2cents

Yeah, these are only estimations. Usually the plants can take longer. As long as you aren't entering cold temps, the plants will be fine and just take longer.

It’s worthless! Plants can’t count! Use your eyes!

should be the average from all the plants they planted but in reality its just marketing and selles usually lie or nobody knows whats the end of flower....

Flower times also depend on if it's an Auto or Photoperiod.
If an Auto says 10 weeks flowering time, then it takes approximately 10 weeks for the plant to be ready to harvest from seed sprouting.
Photoperiods that say 10 weeks flowering time is from the the day they are put in flower, veg time is not included in the flowering estimate for Photoperiods.

Tbh, i mostly ignore trichomes and pistils outside. i harvest outdoor plants when the flower look done lol. Thats as scientific as i personally get with it when im harvesting outside.

take finish times with a huge grain of salt. if you give horizon to horizon sun exposure, even a plant thats normally done 2nd week of september will flower into october without fully maturing yet. give it 4 hrs direct itll likely be done with little ripe buds by first week september. Lots of variables.

You cant totally trust surface trichomes nor the red pistil % outdoors. Too many variables at play, and too much exposure and environmental shifting.

My pb2 has a week or so left, but if you inspected the right flower right now itd prob be 50% amber on the surface. If you cut that bud, dried it, and inspected the inside of the flower though, it wont be quite as far along trich wise as youd expect from the surface or red pistil count. On that plant ive already decided im waiting for the final calyx swell to harvest or weather to change for the worst. And both those changes im expecting within the next week lmao. But only for that plant, she has a couple sisters that wont be done for another month looks like... same cross, same conditions, same exposure.

Had a nearly pure sativa just finish up right next to a nearly pure indica, getting an hour less exposure, that flowers faster indoors, but still looks to have 3-4 weeks left too. Grains of salt all around on outdoor finishing times. Its a total guess in most cases, especially with non stabilized crosses.

I would never harvest on a time-line. I just wondered why they do it.