GM Service Manual Online
For 1990-2009 cars only

If the parking lamps or headlamps have been left on, the exterior lamps will turn off about 10 minutes after the ignition is turned off. This protects against draining the battery in case you have accidentally left the headlamps or parking lamps on. The battery saver does not work if the headlamps are turned on after the ignition is turned off.

If you need to leave the lamps on for more than 10 minutes, use the exterior lamp control to turn the lamps back on.