I also haven't noticed a 'best time of day' either, they're bottom feeders and only surface to investigate objects (saw one hit an asthma inhaler once
) I'd suggest just going where everyone else is and using the same kinds of bait they do, as it's often frequent carp fishers you see around the mucky ponds. Or scout out the lake you like to fish and remember where you see carp as they will usually return to the same spot over and over throughout the day even after failed hooksets.