Hey Brian,
You can start building up now. The recommended amount for Green Sensation is 1ml per liter. Build this up in 3 steps. For now, give 0.35 ml per liter for a week, then 0.7 ml per liter next week, and after that, 1 ml per liter. This way, you let the plants get used to the nutrients, and you can also see how they react. Also, adjust your base nutrients every week so your EC doesn't get too high.
Good luck, man! And if you have any questions, feel free to send a message!
Greetings from the Netherlands 😋