Routines vs. Modes, etc

Most of this functionality is now in the official smartlights feature. Have you had a chance to look at that yet? The “turn off after 20 minutes“ is in the “power allowance” option.

https://support.smartthings.com/hc/en-us/articles/205949776-How-to-create-lighting-automations-with-Smart-Lights

If you want to get fancier, there’s a how to article in the community – created wiki on setting up a virtual timer to use with lights.

http://thingsthataresmart.wiki/index.php?title=How_to_create_a_virtual_timer_for_a_light

It’s true you can do just about anything you can think of with webcore, but that might be overkill for something this simple. So I would just start by looking at smart lights and see if it has what you need. It also has the advantage of being able to run locally, which webcore cannot.

You might also find the following FAQ of interest: