I’m starting to see a few amber trichs. Is there...

Your humidity is kinda low ,could slow it up a bit . unless its a typo on your dairy but I would run 40- 50 % humidity and drop some at end

I'm fully in agreement with my growmie, Hashy, here... I use a PK booster throughout flowering and punch it up even more during the last two weeks... (General Hydroponics Koolbloom liquid for most of the flowering period, switching to KoolBloom dry for the last two weeks)... but you've got longer to go than you think here, as Hashy has said... Good luck!

Also it's the trichomes on the buds you need to keep your eye on. The ones on the sugar leaves develop way faster then the trichomes on the flower.

As your only mid way through flower your fine using a pk booster you have at least 4 weeks left on the plant as your only in your 3rd week of flower.

High, you should not provide a PK booster during late flowering the plant doesn't need phosphorus (P) they only use this during early and mid flowering. But give a K booster instead they need a lot of potassium (K). Next to potassium (K) They need Calcium and Magnesium so don't forget to add a Cal-Mag supplement to your nutrient solution. When 10-20% from the trichomes turned amber the buds are at full potency and then it is time to harvest! Make sure that you look at the trichomes that grow on the buds the ones on the sugar leaves mature faster and give a wrong indication. Also make sure that you look at multiple buds on the plant and different sides and heights from the buds to get an accurate indication when to harvest.

Bloom nutes with plenty of P and K in it or add a pk supplement to your existing nutes.