Rear defroster timer... isn't it supposed to turn off
 

after a specific time? Mine will stay on indefinitely without turning off. I've never owned a car that wasn't on a timer. Anybody know what that time should be?

mines like that too, stays on the whole trip, usually my old e36 turned off like in 15min.

Just read the manual today about this and yes it is supposed to turn off after a specific amount of time. I was researching it because the other day I pressed the button to turn it on and the button got stuck and would not activate the defroster. Once a I got home I sprayed a little WD-40 around the button and it is now unstuck, but now it comes on everytime I start the car and can't be manually turned off.

Agreed. My E39 528 turns off after 12 or 15 minutes. The owners manual for the X5 says it shoudl turn off but doesn't specify an amount of time. Like you, mine stays on forever, unless the defroster cycles off but the button light stays lit. But I doubt that.