You can achieve your requirement by changing the timeline item templates. RadTimeline exposes two properties that you can use in order to change the appearance of the timeline items: TimelineItemTemplate and TimelineInstantItemTemplate. You can take a look at the Customizing Items help article where this approach is further described. Basically, you can create a custom DataTemplate and bound it to one of those properties depends on which item template you want to change. For your convenience, I have created a sample project demonstrating the above mentioned approach.
As another options for displaying the text you can use a tooltip. RadTimeline supports tooltips for its items. You can specify a tooltip template and display the details of the item. The Tooltips help article in our documentation will give you more information about this feature.
Hope this information is helpful.
Regards,
Dinko
Telerik
Do you want to have your say when we set our development plans? Do you want to know when a feature you care about is added or when a bug fixed? Explore the Telerik Feedback Portal and vote to affect the priority of the items