My indoor plants have started to flower while in the 18/6 light cycle. Should I go ahead and move to 12/12 or let them grow for a while?
If the plants are flowering on 18/6 then they are autos. There’s no reason to ever switch them to 12/12.
Good morning 
are you growing autos? It sounds like it if they started flowering on 18-6 light cycle. I believe you can leave your light on the 18-6 if you want. Happy Growing 
Are they flowering? Or do they just have a pistil here and there at the nodes? If it’s just a pistil here and there, then it is more than likely just showing it’s sexually mature, or “lifting her skirt”, and ready to flip when you are. If it’s full on buttons, then it’s likely there a mixup and you got an auto.
Good call. @Moreharv1 can you please post pics?