There isn’t any way to enter a date by typing something into any of the widgets. You can change the slider position programatically by setting the currentTime on the clock and setting the start and stop time of the timeline. Here’s an example:
var currentTime = Cesium.JulianDate.fromDate(new Date(1995, 11, 17));
var endTime = Cesium.JulianDate.addDays(currentDate, 1, new Cesium.JulianDate());
viewer.clock.currentTime = currentTime;
We plan to overhaul the timeline at some point, but I don’t think it’s going to happen in the immediate future.
We have an issue to refactor it here: https://github.com/AnalyticalGraphicsInc/cesium/issues/754
I added a note that it would be nice to be able to select the date from a calendar or by typing it in.