check fishing reports. i think the biggest thing is that when the water/sun is cool, the fish are shallower and probably a little denser. Think about it, you are working only 6ft of water. so in a 20ft by 20ft square area, 6ft deep, that's what, 2400 cubic feet of water you are working. But when it gets hotter and the bass move deeper to get into cooler water/away from light, say at 20ft deep, now you're working 60+ plus away from the shoreline, so the same 20ft width is 20x60x20ft deep, 24,000cubic feet that you are now working with the same lure trying to get your bass.
I've never heard anyone put it that way< i just think it makes sense. but on washingtonlakes.com most of the consistent 'pros' catch there fish from butt crack of dawn till 9-10am.