Hi Aks26,
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.
Best Regards,
Smart HTML Elements Team