Make an input_select with your 3 values. Wrap it in a template sensor (optional, because you can just use the helper where ever you need it, but in case you want a read-only version). Make an automation with a state trigger for the “on” state with a for: requirement (i.e. it will trigger when the input helper has been in that state for the required time). In your action, call the service to set the helper to “standby”.