I just trans. My week old plant into 3.5 gal pot its only 3 inches tall and its been on 18/6 the whole time should i switch to 12/12
You can switch to 12/12 when ever you feel like, but id personally give it 2-3 weeks veg time then switch to 12/12. Upto you though
when you go into 12/12 is up to you. a plant in flowering will double or triple in height. so a 3 inch tall plant wont be that big.