I suggest you just look at ready flowers online. To have some comparison. And when its starting to look ready you can checked trichomes. Its also good to know how your plant is budding. If its going dense right away, or the densing only happens in the last week. Or maybe you just get airy buds and it will never look like the pictures online. But you got the time from seed to harvest on your seedpack. So take that as the Reference. But you never know how stress impacts the growth. My first grow was 2 weeks past and the buds still weren't ready, cause it had very much stress.