Lights on off risk them off

I think it is better 18/6 and try to increase the temperature in another way.

18/6 is optimum for cannabis growth, any longer is basically a waste of electricity. Besides, every plant needs "sleep" and no plant ever has evolved to cope with a torture/unnatural cycle of continuous lighting. 18/6 is a scientific fact, not a random number and has been derived at over 80+ years into research of cannabis. Without "sleep" time, your plants can not undertake certain metabolic processes and to run 24/0 through flowering, you run the risk of having exhausted plants with incomplete terpenes and cannabinoids, due to the lack of sleep time and the metabolic that occur during the night time.15 degrees is about as low as it should go, otherwise growth will slow considerably, so getting a heater may be your best option, but do not, for the sake of our plants well being, run the lights any longer than 18 hours in every 24 hour time period. You will not miss out on any growth, as there is very little extra growth that occurs after 18 hours of light. Hope this helps,... Organoman.

If it goes down to 15°C with the lights off, I would probably run 24/0 but I prefer 18/6 for autos.

The temps are 9.5oc off today but lights on are 23.5oC I allow plants 4 hours rest then put them back on as I've seen blue hue in the leaves before lights on and slower growth the past 48 hours ... waiting on a second heater now

Hey, greets from the Czech rep. temperatures here are about -15 C at night, it’s not good for them you should keep the temperature at about 20-25 degrees C.