How to know when to start flushing before harvest??

Hi all, How do I know when I'm 2 or 3 weeks from harvest time. I have one plant that has been flowering for about 50 days (last three pics). How do I know when I'm close enough to stop nutes and start flushing? I'm guessing it's about time. The some of the buds' hairs are starting to turn orange/brown...is it time? The first pic is of another plant that is sick. I posted a question but didn't get any helpful responses. Any ideas on that one would also be appreciated. I already tried epsom salts...now I'm thinking it's maybe a potassium def. Yellowing leaves and little brown spots. I've tried flushing, epsom salts. no ferts...I'm using ferts again(FF tiger bloom). Thanks in advance for any help with my girls.
Peace

I would say start flushing. IF you are 50 days in I would say they should be almost ready. Good luck

right on,,,start to Flush my friend....i just havested mine 3/4 days ago..i flushed the last 2 weeks of my crop,,weeks 8/9 were the flush weeks, then let here dry out a little, when top of soil is dry CHOP CHOP....lookie lookie...im waiting for it to dry then im going to air tight Jar them for about 3/4 days...My very first Harvest.........

This is my first harvest also. Ratty and Turkster Thanks for the advice. Turkster, I like the way your tool shed is decorated!