When to start flush if looking fo couchlock (Trich Pictures)

[9KtuFK]

i belive u want the trichs to get rusty brown for the couchlock high and cloudy white for the "head high"

Yes but what I'm wondering is how long does it take for a milky trichome to turn amber. I want about 70% of trichs to be amber when I harvest but want to flush with water for 7 days before harvest.

If I want 70% amber, when do I start flushing for 7 days ... 40%, 50%, 60% ????