duration (Optional): Initial duration in seconds or 00:00:00 when Home Assistant starts. Defaults to 0.
Starts or restarts a timer with the provided duration. If no duration is given, it will either restart with its initial value, or continue a paused timer with the remaining duration.
If you call the service, does the state of the timer change to active? Timers don’t keep updating themselves. Try it out with a 10 second duration. The timer should be active for 10 seconds and then switch back. The remaining time only gets updated when you pause a timer.