So i’ve only grown one auto, but what i learned from it is, there really is no timeline of when they should be where in the grow. I’ve seen autos that boast 9 weeks from germ to harvest but that doesn’t seem to happen. You really are at the mercy of the plant. Unfortunately, if it IS a photo and you switch to 12/12, you still won’t know whether the seeds are auto or not. How much space do you have before the plants reach the lights? If they double in height now and will be close to the lights, I think moving to 12/12 is the best option in case they are photo. If you’ve got room, let them ride for another week or 2 and if there still aren’t pistils, switch to 12/12.
Just thought of this as well. You could always do a healthy trim in the hopes of stunting her growth. If it’s an auto and she starts to show pistils, just move your lights closer for flower. If she’s a photo, you still won’t see pistils after 2 weeks and you can move to your 12/12. This is just me thinking outside the box, but ultimately it’s your plant and your decision how to proceed.