How long does it take for the iPhone update

That will depend on the speed of your network connection and whether it’s a full system update (e.g. iOS 15.7.1 to iOS 16) or an incremental update (e.g. iOS 16.1.1 to iOS 16.1.2). The former can take up to about an hour, the latter a few minutes.

Also, if you update the date that a major update is released, servers can be under heavy load and that can make things take longer.