Use the Zooz garage door app, which will handle setting the relay on/off for you. It will also combine a sensor with the relay into a virtual device that can control and sense the state of the door all in one device.
You can also adjust one of the parameters to "Garage Door" mode which will do what you described, when you turn the relay "on" it will click on for 2 seconds then back off again automatically.
I had the best luck letting the app do it for me and set the parameter back to the default.
