GM Service Manual Online
For 1990-2009 cars only

When you open the door, the interior lamps will come on. When you close the door with the ignition off, the interior lamps will stay on for 25 seconds or until the ignition is turned to an on position. Locking the doors with the power door lock switch will override the delayed entry lighting feature and the lamps will turn off right away.

Using the remote keyless entry transmitter to lock the door will not cancel delayed lighting.