How long does it to update

That is primarily dependent on your Internet speed. A minor update (e.g., 14.7 to 14.7.1) is small and should only take a few minutes. A major update, such as to iOS 15 when it is released is probably about 4 GB. If your Internet connection is 100 mbps (which is roughly 10 megabytes per second) the download alone will probably take 10-20 minutes, then more time to unpack and install it. Further, if you do it when it first comes out and you are competing for server access with 500 million users all who want to update at the same time it can take quite a bit longer. So allow at least an hour, 2 hours to be safe.

And be aware that all of these requirements must be met:

• You must be connected to a Wi-Fi network (and not a personal hotspot) unless it is an iPhone 12 series with an active 5G network connection
• The phone must be charged to at least 50%, and preferably plugged in so it stays above 50% during the update
• The phone must not be in Low Power Mode
• The phone must not be connected through VPN
• The phone cannot be in Airplane mode

If these are not all satisfied the update will pause until they are met.