12/12 to force flower, then back to 18/6?

you don't need a dark period at all. Although it is helathy with 20/4 than 24/day, of course. you don't need it to cause flower, though. Flowering in an autoflower is on a biological timer. Normally the darkness causes a hormonal balance shift, then via negative or positive feedback response within the plant, it causes a shift in production within the plant -- from stems to flowers. Don't deprive your plant of light. Each day it doesn't get the minimum DLI, it literally contracts.. it gets smaller.. it starts to die.

No it will not shock it into veg. giving your autos only 12 hours light can reduce its size and yield. It'll be much happier with at least 18 hours light. Anything over this and you may be overspending on energy. Hope this helps. Cheers from beautiful British Columbia

Agree with shag. If it's an auto won't matter what light cycle you give it.

Hi there! Im not certain but if it is true autoflower shouldnt it start to flower on its on time and no matter the Light cycle? I mean Im not sure that you can force them to flower but if you can then adding more light afterwards should not be a problem cos autos will flower even in 24hrs of light