so to clarify some things.
i speak of peak lighting. you can do any combination you want but there are still halide players who do the typical 8 hours.
here is an example of adam's setup at battle corals.
this is with radions.
obviously if you put out half the par of radions, you will expect less than stellar results.
here are mine with evergrow leds.
you can say i keep my lights on from 6am til 10pm. that is 16 hours.
however.....
peak lighting is 11:30 to 19:30 (including ramp up and ramp down) 8 hours. 6 of those hours are what i consider "peak" lighting.
if you have halides and want an instant-on time, 8 hours would be fine.
my par is 1200 1' below the surface, and i know radions pro gen3s are barely 1000 par if you had all channels 100%.
in conclusion. if your par rating is 300 or greater during peak, give them 6-8 hours peak lighting as long as ramping isnt too obnoxious.
if you have 12-18 hours and a slower ramp period, peak hours can be reduced or increased. because you are asking this question, id hate for you turn on some retina seering lights for 12-18 hours, and say its all fine and dandy.
you read between the lines, but i think you have a few options to choose from.