Flush?

[stickymickey]

Hi all. I'm coming to the end of my first successful grow and need a point in the right direction.  The girls have been 9 weeks since flip now and, being bag seed, I have no indication of how long they flower for.  I am waiting on loupe in the mail for a definitive view of the trichs but have an app on my phone which can zoom in close enough to see that almost all have gone milky and the odd one or two are amber. My question is not when to harvest, but when to start flushing? and will the flushing process cause the trich ripening to speed up some? I'm worried that if i flush too early I will lose yield but too late and i will end up with plenty of CBN and not enough thc...