varies greatly.. i've had some really put on the jets and amber up very quickly after buds had fully fattened, and i've seen some plants refuse to amber up for so long that the plant clearly was over-ripened beyond my preference -- the latter of which made me change how i choose when to harvest.
This is why i say learn to use more than just trichomes. They are probably the single best option, but they are not perfect, either.
this may not be good for you, but at this point i use a time-limit baed on what i recognize as fully fattened calyxes -- this depends on perception, so it may not translate exactly for another person. if the colas are unchanging, visibly, i'm generally harvesting within 7 days of that point. If they amber up before, they get harvested sooner, but if limited and seemingly unchanging amber by 7th day, it's chopped unless i see other things that make me uneasy about doing so. If i see it progressing steadily, i'll ignore the 7-day limit. Context dictates. I find this results in more consistent ripeneses across all genetic variance.
I really dislike the flavor of over-ripened buds. You get those extra purple clyxes that are often hollow and brittle (happens to preflowers first, but if really bad, that's seen in the buds, too.) You may feel differently. The primary point of that anecdote is that you will likely need to form a more sophsiticated method that requires experience to compliment simple things like seeing X-percent amber. it's sucks at first compounded by not knowing your own preferences, but once familiar, it's much easier.
Like fertilization, it's something you will barely think about after a few grows... simply observe and react, in this case. Simply stuff is systematic about learning.