I don't know enough about the quickscreen to program this in. What would be an appropriate menu item to make it work correctly?
Edit: This appears to be a bug in the quickscreen code. It doesn't handle menus correctly when the menu counts down instead of up. The threshold menu counts down, so the value is locked in the quickscreen. I've opened a bug report in FlySpray: FS#10636.
Edit: Fixed. The quickscreen menu works correctly.