The general workflow for adding Keys via the Auto Key option is to specify a time in which you want to reach your desired value for your Widget, then moving the Timeline Bar to that time and setting the value via the Details panel or by using the Grid (mostly used for location, rotation, or scale). Once you have set your end result, scrub to the beginning of your sequence and set the default state for your Widget. When scrubbing the Timeline bar between the two time periods, you should see your change occur gradually over the time period.