I have a friend who uses those crappy timers that you press the tabs in and stuff, sometimes he presses one in and its a 15 min per tab so it turns on for 15 min in the dark time during flower that never caused a problem but it was only 15 min not 3 hours he has bought the digital timers and that fixed the problem but I use a sentinal MDT1 and HPH4 and I never worry about it - it will even wait to turn the lights back on if the power goes out really fast so it dont mess up the bulb or ballast
Personally I don't know why this shit is so sensitive to this and that when moon light and car lights don't do shit to it. I am sick of babying this shit. I am fed up with indoor growing its a fucking hassle..and a money pit. I will never do it again. I sowing seeds and waiting to fall. This goddamn shit is ridiculous.