This whole topic on time of day related to what can be caught or what hits is interesting and a lot of good points have already been made. With my 2 cents, I'll toss in another theory.
I tend to think of it more as "opportunities" regardless of time of day. Huh? Let me try to explain lol
Each day of fishing can be segmented into various opportune movements, or flurries, if you will, related to temperature, wind, light, etc. For example, it can be high noon with a stagnant-like water with zero bites and then, out of nowhere, a flurry of wind suddenly ****** the water into a myriad display of diamond like ripples. Suddenly, that big girl slams the lure! I've witnessed moments like this throughout a day which have nothing to do with time of day but more to do with the conditions at a particular moment during a day. It can be the wind, a sudden flurry that pops out of nowhere like I mentioned, or a big puffy cloud passing overhead, or a temperature flux, a front, a fog drift, a storm brewing in the distance, bait movement, birds diving...a host of things. A host of things, day or night, I've seen it like this all the way around. So I tend to look at each day--no matter the time of day--as having great fishing opportunities. The key is in being prepared and positioned to take advantage of those opportunities.