Configurable postpone shortcut buttons

I frequently use the option to modify ring time, but the slider is hard to use for me.

It could be nice to have a possibility to setup the increase step (currently 15 minutes) in drop-down menu, as well as the lowest and highest time for postponing (currently -3:00 to 3:00).

Or allow users to have shortcut buttons with configurable values for more convenient access.

support conversation with Marek