iPhone 7 doesn't update and shows only “estimating time remaining”

To update over the air from the phone all of these requirements must be met:

• You need at least 6 GB of free storage
• You must be connected to a Wi-Fi network (and not a personal hotspot)
• 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, and it may be necessary to delete any VPN apps and VPN profiles
• The phone cannot be in Airplane mode
• You cannot still have a beta version installed on the phone
• You cannot have a previous version that was downloaded, but not installed - go to Settings/General/iPhone Storage to look; if you find an iOS installer, delete it

If you can't meet all of them you can still update using your computer.

Go to Settings>General>iPhone Storage. Let the list of apps load. Swipe to find the iOS software. Tap on it and in the next screen, delete it. Then turn off WiFi in the settings.

Restart your phone again, turn on WiFi in the settings again and download the iOS update again and see if it will install.

You can’t install a previous version. 15.6 is currently the only version you can install. Yes, you can use a Windows 10 PC with the latest version of iTunes installed, which you can get from https://itunes.com.

Restart your phone and try again.