Vibrate only when I'm away

The comment made by @Izzy is correct; you can accomplish it with automation. I am using MacroDroid to demonstrate it.

Assumptions: The screen is off (when the screen is on, you are using the phone).

1. In the Trigger tab, in the Device Events section, select Notification, then Notification Received. Choose Any Application, on the next screen, click OK.


2. In the Action tab, in the MacroDroid Specific section, select "Wait Before Next Action", then set it to 5 minutes (or any appropriate time length).


3. In the Constraints tab, in the Device State section, select Device Locked/Unlocked, then choose Device Locked.


4. Give the macro a name and save it. It will look like the image below.

When the phone receives a notification from any app when the screen is off, it will wait for the amount of time set then vibrates.