What would happen if I take my watch off the charger before the update is done

Hi

Do not remove your Apple Watch from the charger until the update has fully completed.

You may otherwise cause your Apple Watch to be unable to turn on and to require servicing:

If you see a red "!" on your Apple Watch - Apple Support

Follow the instructions here:

Update your Apple Watch - Apple Support

I suggest that you leave your iPhone and Apple Watch undisturbed until the process has fully completed.

Be sure to follow Apple's instructions, including:

• "Leave your Apple Watch on its charger while the update completes. Don't restart your iPhone or Apple Watch, and don't quit the Apple Watch app. When the update completes, your Apple Watch will restart on its own."
• Update your Apple Watch - Apple Support

Keep in mind that Apple advises that it may take up to an hour or so for the update to complete (and perhaps longer, depending on the download speed of your Internet connection).

If the red exclamation mark is shown at the end of the process, then you will need to contact Apple Support (mail-in service may be available, if required), make a Genius Bar reservation or visit an Apple Authorised Service Provider to arrange for your Apple Watch to be serviced:

• US: Apple Watch Service Answer Center - Apple Support
• Elsewhere: Select your country for Apple Watch service and repair information

Otherwise, if the process completes successfully, you should not encounter any issues.

More information:

Get help if your Apple Watch displays a red "!" - Apple Support