"When to harvest?"
That seems to be a question a lot of people wonder when they're growing for the first time. It's definitely something I questioned and had to learn. Just looking at your plants won't cut it. Nor will only doing a flush. Some varieties take more time, this is when you'll need to know how to look at your plant's trichomes.
Hopefully you already have a microscope on hand for checking for mites and such. You'll definitely need one to make sure your plants are ready to go. I used a simple one that fit over my phone's camera like this.
As you can see in the image above, this plant isn't ready to go. The trichomes are still clear and just beginning to get cloudy.
In this second pic, you can see that the trichomes have started to take on a milky coloring. Some almost getting to the desired amber color.
Looking through the microscope also allows you to appreciate the color coming into your plants. Nice deep purples on this Blue Dream. Now the trichomes are starting to take on more amber. You'll want to continue to monitor your plants like this each day as you approach your estimated harvest date. Once you've reached 30%-50% amber, you're ready to go.
The reason you don't wait longer than this, is because the trichomes will continue to change throughout the curing process. You don't want to take your plants down too late, unless you're trying to push CBD levels up in your plant.
Happy harvesting friends!