Hmmm, all normal strains exhibit a roughly 2 week stretch-period when forced to flower with 12/12.
I dont know how auto-flowerers act as I've never grown them, but why would you want to grow autos indoors in the first place?
And, the reason for the change in spectrum is to replicate the conditions in nature, as the spring and high early/mid summer-sun in a clear atmosphere tends towards the blue, and the lower late summer/autumn sun in a dustier atmosphere tends towards the red. And the plants are naturally adapted to follow this spectrum-shift and make the most out of it.
I would for your auto-flowerers just observe them, and shift spectrum when they settle for budding.