Timer plus is a beautiful, simple timer for the Garmin Smartwatch. It will run in the background, so there is no need to keep the app open. Once the timer has gone off, or even while it is running, pressing the Back button will reset the timer. Pressing 3 sec the Up button will lock the keys. Additionally, starting a timer from 00:00 will cause Timer to go into stopwatch mode.Long press up and down when paused - quick set timer. (not supported on some devices)
https://apps.garmin.com/en-US/apps/957fa827-e0f7-41d1-95ea-d543196af1f2