If any of this information is wrong, please say so, it's just a thought.
Vindictus runs a dungeon client-sided, but items/rewards (exp,ap,etc) are server sided. The leader boards were recently introduced, this might be helpful if the game is programmed how I think. Upon completing a dungeon, packets are sent back and forth, yada yada, one packet tells the server it has completed.
Since the LeaderBoards were recently added, Would their be a second packet that sends after the battle-complete packet, or does the first packet contain all the needed details?
:My Proof on this after reading some packets:
Battle took 4:26, but Battle Cleared came up as 5:11 (server lag days), making me believe there is more than 1 packet being sent.
If this is true, wouldnt we be able to stop that packet somehow, or perhaps modify it then send it out? Just a thought..
Edit: Or change the game timer on the top right of the screen (if its using direct values?)