I had one autoflower plant in the same room as a regular plant flowering on a 12/12. It grew comically small and barely produced anything. I would find a way to get it more light.
I was using a 150 HPS along with 600W of CFLS. It had plenty of light to use, just didn't dig the 12 hours of darkness I guess. Or it was a shitty pheno, either way I wouldn't