This is all just anecdotal, but in the last year I turned my lights on for some visitors and forgot and left the timer switch on for 6 days of 24 hours light, had to treat a large infestation of red planaria (the easy ones) and the toxins bleached all of my corals and just last week had my CO2 tank on my CaRx run out and my alk dropped to 4.2. Other than needing a week for the colors to bounce back after the lights staying on and about 2 weeks for the reds to return to normal after the planria poision, I did not lose one thing and growth did not really stop either. Nothing even blinked at the alk drop. I attribute this partially to a super-mature tank, but mostly Metal Halides keeping the corals as healthy as possible all of the time. I would go with your gut here and not think too much... look for the common denominators. 
Yeah, I pay about $30 more a month to run the Halides, but seems cheap to me.
Yeah, I pay about $30 more a month to run the Halides, but seems cheap to me.
