Gelato pistils not turning orange at week 19

I would suggest harvesting according to your plants' trichome coloration since some strains may not develop orange/brown pistils at all or in small amounts! the color ratio affect your buds "high" And the extended flowering period is probably due to the immense radiation stress, and nutrient "lockout" that caused heavy Zinc (Zn) deficiency! Lower your light schedule to 20/4 max and let your plants rest and use the energy they produced during the day to provide growth. Plants actually need some time in the dark to actually burn the energy produced by the leaves through photosynthesis to induce foliar/flower/fruit growth (Yes even auto-flowering plants! with as tempting as it sounds to give your plants as much light as possible sometimes too much light can harm your plants) As for the nutrient "lockout" check the pH of your irrigation solution, you're looking for pH ranging at 5.5-6.5 (if you're growing in soil aim for 6.0-6.5) Make sure you irrigate with at least 20-30% runoff! And lastly lower the "Overdrive" additive dosage to about 0.75 ml/l, and the A&B fertilizers to about 2 ml/l. Try adding a fertilizer in small amounts containing Zinc that might help treat the deficiency. Hope this helps! Good luck and happy growing :)