yes, you can customize the header of the Timeline with any content you wish via the <b>timelineHeaderFormatFunction</b>. Check out this demo on how to use it. You can read more about it in the official API document. Please note that this callback is used to customize both timeline header sections where the third argument in the function indicates whether it is the header details ( top level header segment) or header section that you are currently customizing.
Thanks a lot Chris. I managed to figure it out and it works exactly how I want it to! Just another thing, there is also a row above the months row which displays the year. Is there a way to turn that row off completely?
Unfortunately it is not posssible to hide the header details section of the Timeline header via the official API of the GanttChart component at this time. The header is designed to have two segments. I can only suggest that you to not set content to that section via the formentioned <b>timelineHeaderFormatFunction</b>.