I’m confused, are you asking if the plant itself is flowering already or if you should switch?
In your diary you say it’s an auto. Autoflowering (rudelaris) strains shouldn’t need to have their light changed to 12/12. They should flower on 18/6 just fine all on their own. To get the autoflowering strains we have now, rudelaris/auto strains have been crossed back with photoperiod(Indica and sativa) strains to get higher thc producing autoflowers.
If your plant isn’t flowering when you thought it would, sometimes putting her in the dark for 24 hours will jumpstart the flowering process. Other times you end up with a plant that somehow ended up with more of the photoperiod strain genetics and less of the auto genetics which results in you actually having to change the light period to initiate flowering.