Trick the refiner into thinking it is a date and time MP

trick refiner.js

var propertyName = ctx.RefinementControl.propertyName;
// Let the refiner think it is a datetime field, needed for custom managed properties
ctx.RefinementControl.propertyName = trickDateProperty(propertyName);

// Retrieving the labels
ctx.BucketedFilterData = AjaxControlToolkit.SliderRefinementControl.GetDefaultBuckets(ctx);

// Reset the property name
ctx.RefinementControl.propertyName = propertyName;



function trickDateProperty (prop) {
  // Check if the property does not contain the OWSDATE suffix
  if (prop.toUpperCase().indexOf('OWSDATE') === -1) {
    return prop + "OWSDATE";
  }
  return prop;
}