Just based on what ive seen with the Autos i have run before if this is an important grow i would do 24/0 instead of 20/4 and i would also give it 48 hours of dark before harvest just like with regular plants. Also what size containers are you using? The ones i used were about 1.5 gallons, i have heard that they do best in 1 gallon containers and stay with the breeders timeline better in the smaller containers. If you are on 20/4 and they havent started flowering yet maybe try to keep uner that cycle until they show preflowers then put it on 24/0 ( if you like to experiment). I dont know what kind of effect lengethening the light period when a plants starts flowering would have but with autos i dont see where it could hurt, but like i said if this is an important grow or you only source of meds id maybe switch to the 24/0 if they havent been veging long otherwise keep them on 20/4. I currently am starting 16 various autos in 1 gallon containers under a 400w (thinking about putting a grow diary thread up) and i think the 20/4 veg, 24/0 flower cycle is what i am going to try this time to see what it does because i have heard root growth is better at night (if i am worng please correct me)so those 4 hours of dark durring veg could help boost the yield and/or help them to start flowering a little erlier.