RadTimeBar for Silverlight does not visualize the data that you describe. I suppose you have added a content control to the timeBar and this content control visualizes the data. The content control that you add to the timeBar does not influence the interval display in any way. Basically, you should get the same interval display on all zoom levels with a timeBar with content as with a timeBar with no content. That is why, changing the data in any way will not give you the described result.
In short, manual control over the currently visible interval in the timeBar is not possible. Basically, the timebar can display hundreds of years at a time in the viewport and automatically calculate what is the best drill level that it should display for item and group. If you set it manually there are 2 options - display the new levels anyway, even if they cannot fit on the screen, and zoom-in/out automatically to show the new drill level. The first one can be a little bit dangerous and can lead to a severe performance hit, because setting the current drill level to Day when you are viewing a period of 100 years can result in too many boxes.
Additionally, due to a limitation in Silverlight framework, we have enforced a constraint for zoom-in to maximum of 30 000 pixels. As a result of this constraint, the timeBar might not visualize some intervals in its Intervals collection.
All the best,
the Telerik team
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