problem in flowering period

If the power goes out, and there is an extended dark period, will this have any large effects to the plants if they are in the flowering period?

Yes the effects can actually be devistating. If the plants are already in a twelve twelve than they are reacting to the light the same they would be reacting to sunlight in nature, and the sun is always on time. Unfortunantly if you fuck with their photoperiod too much it can confuse and stress the plant into trying to produce pollen as a last ditch effort too reproduce. This could turn your plants into hermies, and that's just no good hopefully this is just a precaution and not happening too you right now. good luck man

Dont worry too much, I think people way overstate the risk of hermies. Iv ABUSED plants to no end; had bad photoperiods with light towards the end of the dark cycle, bad pH, bad nutrient burn, bad nutrient lockout, burnt them with lights,etc and Iv NEVER had a plant hermie on me...all with feminised seeds to start off with too. I even had a plant that got random hours of light cos I was flowering it in a tent with autoflowering plants and had to move it into the wardrobe to avoid 6 hours of light...however sometimes I didnt make it home to put it in the wardrobe, sometimes I forgot to put it in the light for days at a time. Flowered perfectly, savage bud, 2 1/2 - 3 ounces off that one plant (LSTing helped alot Im sure). So dont be too worried if its just a one off for you, plants have to react to unusual light cycles in the nature too.