The leaderboard will rank you after the slowest run you have made that week.
Here's a page of the leaderboards from right now
The 11:57 is the slowest run the current top contester -dicht.PinkGuy- has made this week.
Data (recorded from DE's database http://content.warframe.com/dynamic/trialStats.php) shows his fastest time for this week as 11:50.
This issue seems to be caused by the ingame leaderboard ranking the players after slowest recorded time for the week an