Class C (former "Class IV," aka "graveyard") stations on 1230, 1240, 1340, 1400, 1450 and 1490 generally run the same power level (usually 1000 watts) both day and night, non-directional.
What makes the difference between daytime and nighttime reception isn't the signal a station like WBCB is putting out - it's everything else that's coming in. Once you start getting into the "critical hours" around sunset, skywave reception of the hundreds of other stations on those channels becomes possible, and even if any one of those other stations produces only a tiny amount of incoming skywave at any given location, when you have several hundred 1000-watters on each channel, the result is a dramatic increase in the noise floor that the local station has to overcome to be heard clearly. That situation persists into sunrise, and often for an hour or two after sunrise as well, which is why at this time of year it can be 8 AM or later before a listener more than a few miles from WBCB can get clean reception.