The vehicle has a battery saver feature designed to protect the vehicle's battery.
When any interior lamp is left on and the ignition is turned off, the battery rundown protection system automatically turns the lamp off after 20 minutes.
This prevents draining of the battery.
Chevrolet Cobalt Service & Repair Manual. 2007-10 Cobalt & G5
w/2.0L & 2.4L Engines
Warning: Gasoline or gasoline
vapors are highly flammable. A fire could occur if an ignition source is
present. Never drain or store gasoline or diesel fuel in an open container,
due to possibility of fire or explosion. Have a dry chemical (Class B) fire ...