I know that this is not true in SW Ohio...During the summer, the only time I fish is at night. The Crappie will feed from dusk til dawn while the air temp and water temps cool alittle.
All along the feeding flats you will see top-water action as they and other night predators drive shad or small baitfish into the shallows.
Crappie have the second best night vision behind Walleye.
Most fish take up to an hour or so to switch from "Day" vision to "Night" vision, they will switch from Rods to cones, or vice versa....Crappie switch from Daytime color vision to Night-time HD Black and White. It takes the same time to switch back in the morning. Maybe this is what you are finding...The Switch-over!
I fished at dark last Friday and just tore up Crappie...and most were larger fish which are now feeding at night. During the day, most people are only catching dinks that are feeding,