It doesn't take that long to install the update. On my Lumia 1320 it takes a maximum of around 45 mins. Even I'm not sure why because on other Lumia's it gets installed really fast. I have noticed many other users also complaining that on the Lumia 1320 it takes long and a couple of them faced the same issue as you.
If you have a SD card installed on your phone. Try removing the SD card, do a soft reset and see if that works.