Don't stress 4 hours is nothing just go back to your normal lighting they wont even notice long as its not out for a week you will be fine all the best
They'll feel the stress. But, you would have to fuck with the light schedule like this everyday/night for a week to send her back in veg. Just plan a bit better next time.
No it is not going to hurt your plants at all, I live in a very Rual area power goes out all the Time and for sometimes Days, So I bought a generator and use that when power goes out, Its better to be in the dark than too much light. Just remember to Reset your timers if you don't have Battery back up on those, you want the timers back in normal 18 and 6 Unless you do a 24hr Veg then that is what you do. So don't worry a day won't matter in that stage of your Grow, Hope that helps you out, And Good Luck, No Worries