That will be easy to do, using a virtual switch, a rule and the Google Home built-in App along with your dashboard of course.
Start by creating a new Device from the devices page, selecting Virtual, giving the device a name and selecting Virtual Switch as the driver (Type). Once created you will see the device appear of screen where you can adjust it's Preference settings, including one to turn the device off automatically. Turn this option on and use whatever timeout you want, half a second should be fine.
Next create a rule. I tend towards Rule Machine, but any of the simpler one's should work as well. Trigger the rule on the new Virtual Switch turning on. Set the actions to be adjusting your devices like you described.
Lastly, add your Virtual Switch to your dashboard using the Switch tile template and add the Virtual Switch to Google Home App on your HE hub.
I've got a bit more brief in my instructions towards the end. If you need some more details let us know.