ive had this happen to me before,, under 72 hrs without light and u wont notice at the end. try not to let your room go under 15 degrees celcious and it wont affect the root system.... top tips..... if you have a gas room heater that will work fine in there as long as you leave some air flow.. also maybe you have a camping heater? their small and cost only a few coins, and they will deffo raise the temps in there for small periods of time as they use tiny bottles of gas ( please dont set yourself on fire).