Does any one know how long it should take for a back window demister to clear the mist? It takes my corolla around 10 minutes, I had it checked by the dealer and they say everything is working fine.

You would not want this feature to work any faster as it would harm the glass and possibly crack the glass if the window defogger was used in well below freezing temperatures. 10 minutes is about right.

Fair enough, thank you for your help.