Both previous posters are correct.
I DO have bad news for ya though... this weekend, the power at my place went out for 7 hours PLUS it flooded- over an inch of water on the floor- a waterfall when you opened the back door... good times.
Trust me your half hour light difference in veg isn't the worst thing that can happen
Just be certain that during flower, if you have a power outage, yank the plugs until you are certain the power is back on and going to STAY on, and adjust your timer to read the correct time before starting everything up again. More dark is FAR safer than more light!