After you download the shortcut, you can hook it up to run whenever a certain alarm alarm goes off like this:
- Tap on the Automations tab at the bottom of the Shortcuts app
- Tap on the blue plus button in the upper right corner of the screen.
- Tap "Personal automation"
- The next screen gives you a list of events that the phone can recognize. You can choose whichever you want. In this case I suggest "Wake-up alarm" under "Alarms".
- When you have the alarm selected tap "Next" in the upper right.
- Tap where it says "Add action". In the search bar enter "Run shortcut". Tap on the corresponding icon that appears.
- Then tap where it says "Shortcut" in light blue letters and select this shortcut from the list. (Congrats, now you know how to make a shortcut!)
Once this is set up this shortcut will set a 20 minute timer every time your wake-up alarm goes off.