Can I temporarily set Autoflowers to 12 hours of light to make them flower faster and then switch back to 18 hours of light during the flowering stage? Please respond quickly :)
Why autoflower then? There are stimulants that can trigger flowering and many regulators. But in my opinion, you should stay away from those if you don't know exactly what you're doing.
It has no effect on flower time for an autoflower.
If your autoflower is not flowering (greater than 8 weeks since sprouting) you may have a photoperiod. Accidents happen.