For some reason, sometimes it defrost REALLY fast and sometimes it takes over 20 minutes. IS THAT NORMAL??? The rear defroster button doesn't automatically turn off until 30+ minutes. The manual says 5-10 minutes...

 

For one I have never experienced window tint affect the defroster. The defroster wires are still in direct contact with the window with the tint just being over it.

For two if you are getting that much variable there is an issues. It should be relatively fast. 20min sounds like it's not working, and then eventually turning on. Take it to the dealer.

 

Usually tint speeds up the defrost, retains heat

 

If the tinter cut a wire while trimming the film, you could have that problem.

 

^^+1

Perhaps intermittent contact in the electrical circuit on the glass

 

aaaaand the dealer will say 'can't diagnose with the tint on, remove it and come back in..'