I had that problem and the only way I got around it was to aim the cameras at an area that had the front porch and back porch lights on at night with a neat light switch that has a timer that turns them on at night and off in the morning.
Are the cameras the Xfinity Icamera2 or Icam? If so then they should have IR. You should be able to see 40-50 feet in total darkness with them. Look at the cameras when it is dark and there should be red lights showing. If not then there is something wrong with them.