How much time ?

I wouldnt lollipop this late into flower. I would say you should have been taking the undergrowth bit by bit within the first 2 weeks of flower so as not to stress it out during bud production. With re. to chop. Get yourself a microscope doesn't have to be expensive but it will give you a great indication of when the Trichs start turning from clear to cloudy to amber. I would look to start flush at 20-30% amber. Then after 7-10 days flush hope to have roughly 50/50 amber/cloudy.

Btw first time grow!