Normally, a night vision potion will start steadily flashing the sky background it's 10 seconds from running out.
A night vision potion edited to a really long length of time (I'm using it for a spectator mode in a map) will start suffering from a constantly flashing background at points during it's duration almost like it's stuck at 0 seconds left on the potion, when there's really tons of time left on it. It flashes at an extremely high rate and is hard on your eyes.
-Set a command block to do: /effect @a 16 9000000 0
Example in this video: