You can specify specific times where you want the volume on the speaker to be lower using a feature in the Google Home settings called “Night Mode”. That way, you can set the “Night Mode” to work around the time of your choice, when you are typically in front of the TV (and that speaker) and go back to normal in the morning when most people typically are getting ready for the day.
To get to it, open the Home app and then select the speaker you’d like to set a night mode on. From the speaker’s page, select the gear icon in the top right corner, and then select “Night Mode” from the next page of options. Toggle the feature on to bring up a calendar where you can schedule days and times for Google to be quieter than usual. You can set the max volume for the speaker to the perfect setting for you, and also adjust the brightness of your device’s LCD, if you happen to be using a Google Home Hub. Which happens to also be accessible to blind and partially sighted users.
Also on this page, you’ll see a “Do Not Disturb” feature. That will block sounds from reminders, broadcast messages, and other notifications on the speaker while Night Mode is enabled. Toggle that on/off depending on your preference.
Once you have it set up, your Google Home will adjust its volume based on your personal preference, so you don’t have to handle things manually anymore.