Such beautiful plants. I hope I am as lucky once mine get close to harvest! Are you using CO2? They look so close to harvest I wonder if they will wait until May?
Note using any CO2, but I do have proper ventilation at all times. Most people don't realize that proper ventilation doesn't just mean making sure they have good airflow, but making sure they don't have TOO much airflow.
I have a 6" fan and I have the dial in the middle of the low section. A lot of people will crank it up, but when the tent closes, it becomes a wind tunnel. Which is not always good for the plants. The key is to make sure you are cycling the correct amount of fresh air in, and not over doing it.
The room the tent is also has negative air pressure. So the air in the room is constantly being refreshed, so what is pulled into the tent, is not stale.
I also like to take a small sample, starting about 3 weeks from harvest. I took one today, and dried it in the oven at 200F (never higher). The smoother it becomes, and the more "chill" the effect is, the closer to harvest. That in combination of looking at the trichs with a microscope are how I decide when to harvest.
A lot of people will claim "wait until it's milky, wait until it's 25 percent amber". This is a good rule of thumb, but as you grow more, you realize the effect you like does not always go along with trich colors. It is better to sample and harvest when you feel it is best. This is how I eliminate all paranoia with any strains I grow.
If I was growing for just high THC and potency, I of course, would go strictly on trich colors and let them go as long as needed.