i do it anywhere from the end of theyre 12 hr dark cycle, moved em to 24 - 48 and even 72 hour dark periods ... Stress doesnt matter because its a finished product, all a dark period does, is mature resin glands, in which turn the "tri's" nice and dark .. The longer the dark period the darker the trichromes. I put em in the with tri's milky with a red top, come out two days later completely dark red and beige. Dont put them into dark period wet, always have soil almost bone dry, this helps with drying time as well .. Dont want dark tri's, put them in a 24 hour dark period, as soon as the trichromes head turned beige .. this will give you white stem and red head, for an all around high ..