Trichomes are White, how long til 50% amber?

I'm debating on whether or not I want to fertilize again. I stopped fertilizing about two weeks ago because I thought it would be time to harvest by now; however, I'm just now getting close to 80% white(cloudy) trichomes. My question is, do I have time to fertilize the plant one more time and still have 10 days to flush with fresh water? I'm worried that I wont have enough time to flush the plant before I reach 50 to 80% amber, which is when I'm wanting to harvest.
I'm sure can be very different per plant but:
How long, on average, does it usually take a plant to reach approximately 50% amber once you start seeing the first sign of amber trichomes?