Horizontal bar using timeline or Gantt

I am trying to use the Chart Maker to create a Gantt type chart.
Would you please explain how to define start and end date ?
Regards,
Eytan

I am also struggling to determine the best way to successfully pass the JSON of the start and end dates to properly render the data on the gantt chart when building upon an existing template.

…?Data1=[startdate1,enddate1],[startdate2,enddate2]…

Would love to know if this has been solved. Thanks!