About an hour after it goes dark at night seems to me to be best.... fish have been hiding out and not feeding as well during the day... get hungry and as soon as it goes dark develop the confidance to really start to feed.... morning darkness and the fish have been feeding all night and so in my experience it drops off....
As already said though, if the fish comes across a nice bit of food it will just wolf it down, daylight or darkness! I would guess the mark you fish has a massive influence.