Why?
What model?
Especially if you're wanting to "restart" when you come back?
NO one, including me, can estimate when something will be done within 20 min. Okay, maybe I can for some things
I'm just trying to understand what you're trying to accomplish with a timer? Start it go away and have it done when you come back?
Better to get an AQ or something with a specific method of doing that (it has a remote probe that will go to hold when it reaches your target temp.
Tell me more so I can help.