Just a note... you actually have to BEAT 0:0:0 and go into negative time to get the sigil. If you get 0:0:0 exactly, you won't get it.

Also, if you haven't got Caladbolg already, if you go down to the bottom of the screen and find the trainer there. Race her, and whether you win or not, the man who usually guards the path to the ultimate weapon at the top of the map will be standing there - from my experience he is always there when you do this. Run up there and grab it while you can! You may be able to board a chocobo first, but I can't guarantee that he'll still be standing there once you're on. I ran all the way across, but I have Peaceful armor so it wasn't such a pain.