Your plants couldn’t care less if they get 10hr @60% or 6hr @100%. A photon is a photon. Light energy is accumulative.
Personally I don't think that is true and certainly not for all plants. Plants requiring high-intensity light will not receive it no matter how long the lights are on. If that was the case there would be no reason to buy stronger lighting when you could just run your weaker lights longer (which would please most people.) When plants are shaded in our tanks or even outdoors some will die off even though they are receiving some light all day.