20-25 minutes is asking for trouble, but in the long run- don't be to hard on yourself. My wife leaves ME and our DAUGHTER in the car for 45 minute shopping trips minimum!
(Nobody comes running to save us!)
...editors note- I listed "ME" before my "Daughter" (while grammatically incorrect) to signify that my wife doesn't leave my daughter by herself in the car so nobody feels compelled to call child protective services.... and such is the crux of the matter. Today's society, it's not a good idea to leave anything inside a car (well- maybe except a husband) for any length of time whatsoever!