Some breeders qualify the projected time by saying "under ideal conditions."
Of course that is useless since they don't tell you what those conditions are. Might help.
I chopped my last plant 20 days after the indicated 70. And I chopped before she was really at her peak. My first grow was another 70 day variant. Ran over 100 before I gave up and chopped.
Current plant is already 10 days past the projected date. Though it is close.
I use the breeders projected date as the point where I start taking a closer look at the flowers every day or three. Once a few trichs start to flash over to amber, I know I can chop now or wait another week or two.