The burning time relates to lots of conditions including the devices and the data volume. For example, the capacity of your computer and iPhone, the amount of data to transfer, backup and restore, network status and other software running on your PC will influence the operating duration. It can be several seconds to more than an hour. But don't worry, it will not cost too much time under normal conditions.
If you want to speed up the process, you can try to close down other running software, restart the computer, change into a stable and faster network, optimize the hard disk, etc.