Rhino got it right. The only reliable indicator is trich color. So I count days only so I know when to pull out the digital microscope or plan for flush
so if you have fluffy buds with a ton of white hairs but with amber trichs you just chop? rather than waiting another week or so and gaining 15%+ more weight and a higher quality flower overall?
I don't know about that, id say the only reliable indicator is experience. both with individual strains and as a grower. your trichs will not mature at the same time on the entire plant either depending on grow style. if you chop when your tops are at 30% amber, your lowers are most likely nowhere near that, are you willing to give up the lowers turning amber at the expense of another 10% of amber on the tops? You are acting as if its black and white when its really a shade of grey and highly dependent on strain IMO
I only count the days of flower to have an idea when to flush (clean water with minor amendments). It is a ballpark and i know 10 weeks we are pretty much there. I also check the trich colour but you can usually tell by the way the buds look. The lack of white pistols and such. The colouring of your pistols changes. The density of the bud changes etc. And I look for amber trichs around then
this is basically it if you don't know the strain. and its all preference too. some like a little early, some like a little late. The flip date is just a guide so you know what to look for. The times given by seed companies are just a guess as there are multiple phenos unless you are working a really stable line with multiple generations of testing, which is not how most of the seeds are with all the hybrid crosses going on right now. there could be 5-6 sets of genetics in any given hybrid cross from 80% sativa to 80% indica depending on which traits were passed down.
the only way to know exactly which day to chop is to run the same cut multiple times and take samples at day 55, 60, 65, etc.
and if you're always starting your day 1 as the flip date, and not when you see pistols, you will always have the same start date and so you will have 1 less variable. why would you add in another variable to the equation that has an element of human error to it? you put it into flower, that's day 1. Now any adjustments you make in the future are always from the start of flip. Its a much more scientific method to say day 1 is the day you flip to 12/12