Accoring to oldskoolgamer, the level was in fact played 4 different times, each for a different mission.
In Sand Ocean, there's a way to stop the clock in one part of the level, so the current ideal run for every mission starts out the same: get to the time stop as fast as you can, then play the rest of the level as normal. 30.29 is apparently the best time possible, and that run was replicated on each mission.