Timeline headers currently have the option to set a TimelineHeaderDateFormat.

https://www.telerik.com/kendo-angular-ui/components/gantt/views/#toc-formatting-the-timeline-headers-date

It's still not possible to set a custom template to show additional text or more than one group header.

It would be nice to have something like a TimeLineHeaderGroupTemplate and a TimeLineHeaderColumnTemplate just like similiar kendo controls.