Problem: two girls one tent, 40x40, an Auto and a Photo, both ~30 days old. Poor decisions and bad planning got me into this How would you proceed?

if your light is powerful enough for a 12/12 photoperiod, just put both on a 12/12 schedule when the photoperiod is ready ... otherwise your photoperiod will never flower. there's not really any other choice and slowlyreducing hours of light isn't going to help the problem. if you wait till the auto is done, your photoperiod will be a monstrosity... or rootbound AF by the time you get to flower. this won't hurt an autoflower if you provide the same DLI over 12 hours as what you did over 18. no worries. these plants aren't actualyl much different except for the trigger to flower. one is dark-dependent and one is not a photoperiod plant, i've always fed them teh same and had exact same results as a photoperiod. the amount of nonsense out there is astounding.