To quit the app, it is a two step process. First you have to pause it then it will give you the option to quit.
To pause the app you need to tap on the Shield icon in the left upper corner and tap on "Stop Protection". HSS is now paused for 15 minutes by default. You will have the opportunity at this time to select for how long you want HSS to remain off.
Note: If you select resume in 15 minutes or 1 hour and your phone has been off in sleep mode for more than 15 minutes or 1 hour the HSS will still turn on when you wake up your phone.
Now that HSS is paused, you have the ability to quit the app. Tap on the Shield Icon and tap on "Quit". A prompt will appear asking if you are sure to quit, tap OK and the app will close.