There is an exploit people use to get insanely low rankings that involves pausing the game to stop the timer and then unpausing and solving the puzzle. The online rankings mean nothing until they fix that.
Yeah, obviously it's not possible to get a time of 0:00 on any level in the game, though I hadn't heard of the pause cheat before. At one time I made it to about 5th ranking on the last and hardest course, but I've probably been knocked way down by now. The times above me seemed impossible to get, at least for me, but I doubt they were cheats or they would have been much lower, if not zero.