Update Apple Watch serials 2

The WiFi/internet connection required is for your iPhone, not the watch. Everything is controlled from your iPhone except putting the watch on charger power and maybe entering the watch passcode on the watch (new requirement added in the latest update). The only reason the download will pause is your phone loses its WiFi connection (timeout?), or the internet connections and server are very busy (outside your control) and running slow.

Please see Update your Apple Watch - Apple Support, set it going and let it complete without interference. Note particularly the instruction which appears on your iPhone, NOT to disconnect or restart until the update is finished - Very Bad Things can happen after an aborted update, up to and including a watch which never works again. If you are watching the download timer estimate don’t worry about it because it can go up and down from many hours to minutes (and back again) depending on speed checks every few minutes.