I’ll let you in on a secret: sliding the Bluetooth toggle to the OFF position in Settings
→ Bluetooth on your iPhone will speed up watchOS software updates dramatically.
But why does turning Bluetooth off accelerate the update process?
Because Apple Watch defaults to prioritizing Bluetooth over Wi-Fi whenever possible in order to conserve as much power as possible. While Bluetooth does require less power than Wi-Fi, the protocol is significantly slower in terms of data transfer than most Wi-Fi networking standards
Disabling Bluetooth on your paired iPhone at the right time will force your Apple Watch to connect to your iPhone via the faster Wi-Fi protocol.
Unlike other Apple devices, your Apple Watch does not download watchOS updates itself.
Updating your watch happens through the companion Watch app on your paired iPhone.
Your phone downloads the latest watchOS update and sends the installer wirelessly to your wrist. Sending that much data over Bluetooth is insane—watchOS updates typically weigh in anywhere between a few hundred megabytes to more than a gigabyte.
Making the weakest link—sending the installer to your watch—faster by temporarily disabling Bluetooth shaves off a significant amount of time from the update process.
However, you must shut down Bluetooth in a specific moment during the update process.
As I said, Apple Watch software updates are handled by the Watch app on your paired iPhone. Among other thins, it automatically retrieves the latest watchOS software from Apple’s servers as soon as it becomes available to download.
The Watch app then sends the downloaded installer file to your wrist-worn device over the air. The watch takes it from there, unpacking the installer and applying the update.
Seeing a rough estimate of the time remaining (for example, “About 9 minutes remaining”) means the app is sending the installer to the watch over Bluetooth.
Don’t disable Bluetooth until the time remaining estimate appears
Keep in mind that it could take from several minutes to an hour for the update to install onto the watch, depending on your exact Apple Watch model, the update size and more.
I know shutting down Bluetooth feels like a cheap trick.
In fact, many folks know about the correlation between Bluetooth throughput and the watchOS update speed. But, trust me: once you try this simple trick you’ll never install