It gets longer based on how much data there is on your phone. When I had a 16gb SD card and only 7-8gb of music and movies it was OK. Now I have a 32gb SD card and about 16-17gb of music and movies and it takes a lot longer.It takes 45 seconds from when I press the turn off usb storage button to when the phone changes the screen back to connect usb storage and begins media scanning.
That seems like longer than it should take.