Agreed...bad habit to get into. Flowering plants tend to freak if you wake them in the middle of nap time.
The only thing I can think of that will possibly fluctuate enough to worry about during the dark period is temperature. (and CO2, if running it) But you can check on 'em just before lights come on without much worry. I'd say no more than 5 minutes before lights on, but this is my own arbitrary guideline.

emptyfarmer420:
Which shade of green works best? Do you use a special bulb?