When reviewing last-second shots on the video monitor, do refs go by the clock or the backboard light? The NCAA changed the rule in 2004.

When officials are required to view the monitor before making a final ruling, the determining factor as to whether the ball was released before time expired shall be when the game clock shows 0:00, provided that the game clock is visible on the monitor. This rule change clarifies game-ending situations.

Why did they change it?

The rationale is that using the reading of 0.0 when it's visible on the monitor, which indicates that the game has ended, factors out the time lag that occurs when that reading sends an impulse that triggers the mechanisms in the light and the horn.