I find it works better at night.
In Washington, many highway lane markings are just rows of dots, not stripes of paint. During the day they aren't contrasty enough for autopilot to recognize them as lane markings. But those same roads at night, with the dots reflective in your headlights, are recognized just fine.
It works better at night in general due to the higher contrast and lack of sharp shadows--it's easier for the cameras to pick out the lines from the rest of the scene.
But you have to be careful in certain situations, such as when oncoming headlights are shining brightly at you--particularly if there's moisture in the air and the windshield is fogging up a bit.
To my knowledge the autopilot camera sensor captures the visible spectrum, not IR...but I could be wrong about that.
Unless the camera has a very good built in IR filter, it will capture IR also. The IR spectrum is very close to the visible light spectrum, and blends in at higher wavelengths.
The AP camera may not be an IR camera, but a side effect would be it capturing/seeing IR. You can try pointing a remote control at your cell phone camera, and take a photo (I don't think cell phone cameras have sophisticated IR filters, though I never checked...) and you should see a beam of light.
+1. I love it at night as that's when I struggle the most with depth perception and changing lanes, but it does an amazing job.Autopilot works fantastically at night! Used it the entire way to Vegas and back this past weekend with no issues. The lane markers are really reflective and get picked up by the system better than during the day in my experience.