I would say chop her in 3 weeks and start the flush within 2 weeks.
Don’t just watch for pistills. You need to consider the thricomes as well if they are starting to get amber or if it’s till a lot of clear ones.
You may consider the color of your leaves before you start to harvest. Some plants tend to change color the last week of flower so that’s a perfect sign to start the flush.
But from what I’ve seen on the pictures I say flush in 2 weeks and harvest in 3. Good luck my dear friend and I hope your buds will taste amazing 😍🤩