Your "night lights" aren't really night lights - they're actinic lights. They're the same as your "day lights" but are just putting out light in a different color/spectrum than your "white" lights. You don't want to run actinic lights all the time - you want to run them in conjunction with your white lights. Most folks that want to simulate a dawn/daylight/dusk cycle do something like what cooltop mentions. Now if you're talking the small LED
"night lights" - those are OK to leave on 24/7.
Just to give you an idea, here's my setup...
9:30am - actinics on
10:00am - 10k (daylights) on
8:00pm - 10k (daylights) off
9:00pm - actinics off
I also have 2x 1/2W LED
blue "nightlights" that stay on 24/7.