Does your plant have pistils (white hairs) on it?
The trichomes (resin glands) should be visible when the plant has white hairs or shortly after. You will see the resin glands on the small leaves around were the buds form. When you say your plants have been in the flowering stage for a month, do you mean that you changed the photoperiod to 12/12 a month ago or do you mean that they started to flower a month ago? Because it usually takes about 2 weeks of 12 hour days before you see any signs of flowering.