it's not being touched by the large piece of food that would stress it out, it's the digestion process. digesting a large amount of food all at once takes a lot of energy.
are you referring to the coralife colormax lamp that is 6500k? are all the bulbs coralife lamps? check into ATI lamps. they will allow you to squeeze every bit out of that fixture you are using.
if that image you use as your avatar is your current tank, you can see it appears a bit yellow. this is from that colormax lamp. it's not going to hurt anything, but i think you'll be alot happier with some high end lamps.
if you don't mind spending the money, try ATI blue plus and aquablue specials. if you can't find ATI lamps locally, giesemann bulbs are also high quality.
as for the on off question- corals don't benefit from a morning evening transition. turning them on all at once and off all at once will achieve the same goal. the morning evening transition is just for humans to enjoy.