if the remotes are set for direct IR out, I suspect this means you have a plasma or CCFL backlit display in that room: at night, the IR noise emissions from the display are so strong (it bounces off all the walls) that the IR commands from the remote are down low in the S/N ratio, and the TV does not receive them

try a test to confirm this theory: at night, turn the display off and see if the cable box now responds