ICloud backup iPhone 5s 16g?

This is my first time backing up my phone in 2yrs I just got a new iphone and I need to back it up and it's saying it will take 8hrs Is it really going to take that long? Or is that just a estimate?

It all depends on your internet, I highly recommend plugging it into iTunes on your computer and doing a backup to your computer, it is much much quicker as it doesn't depend on your internet speed.