RTA time is used in the leaderboard instead of IGT, because it is much simpler to compare between runs. To quote the developer:

[quote] The timer goes up whenever the player is playable. So it starts when the first small cutscene of the game is finished, and ends when the final little cutscene is triggered (so that's a bit after the yellow arrow). The timer is paused during all cutscenes and textboxes, and it still saves when dying or quitting the game. [/quote]