To answer your question. Depending on how full your phone is can determine the length of the back up. For me, a typical 128 GB unit that's full of photos took 2.5 hours to back up to the PC. So, if you're unit is full, then it will take time.
Fastest and safest way for me is always on Itunes.
Side Notes*
Make sure itunes is updated.
Check the iOS on both devices. If Old unit has a greather iOS than the new one, the new one will need to update before able to restore.
Select My Computer when backing up.
Check if you have enough space on your PC to back up all the content.
Do not Encrypt, I've had other customers have this issue.
Make sure you know your password for Apple ID, it may ask for it.
Good Luck