Hey there. I'm going to try to respond based on my experience. From my experience, a cannabis plant is much tougher than you think when it comes to total darkness, as long as it’s not repetitive. Here’s what I’ve noticed:
1. The safety threshold (24 to 48 hours)
Personally, I've had power outages or timers fail for 24 to 48 hours. Result? No drama. The plant just goes into "pause mode." During the vegetative stage, it might stretch a tiny bit to look for light, but that’s it. In flowering, it’s even sometimes used (48 hours of darkness before harvest) to try to boost resin, so no panic for a day of darkness.
2. The real danger: Beyond 72 hours (3 days)
That’s where it gets tricky. If the darkness lasts too long:
In the vegetative stage: The plant might realize that the days are getting shorter and trigger an early pre-flowering.
In flowering: It’s water and hormonal stress. The major risk is hermaphroditism. The plant panics, thinks it’s going to die without reproducing, and can produce "bananas" (male flowers) to self-pollinate.
3. The critical point: Humidity
My real feedback is that lack of light is less serious than stopping air extraction. Without lights, the temperature drops, humidity skyrockets (especially in a closed box), and that’s where botrytis (mold) sets in on the buds in less than 48 hours.
My advice if this happens to you: If you have a power cut, don’t try to compensate by leaving the light on longer afterward. Get back to your usual cycle as if nothing happened as soon as the power returns. Cannabis especially hates it when you change the time the light goes off! I hope I was able to help you a bit. Have a good day!