fast versions are regular photoperiodic plants that were crossed with ruderalis just for one generation.
so when you take a regular indica or sativa and cross it with a ruderalis plant you’ll get fast version, they still rely on photoperiod to flip to flower because photoperiodic genes are dominant over ruderalis which means you’re gonna have to flip them to 12/12.
in outdoors they will flip to flower as nights get longer. when that will happen depends on your exact location on earth more accurately your lattitude. when nights are 10hrs or longer they will probably start flowering but they may start a little later when nights get even longer.
you can easily find your day and night hrs for your location by doing a quick google search.