There are no such events. However, depending on your logic and the order of the executing of the operations, I could suggest you some approaches:
1) If the VisibleRange is bound through a ViewModel, you could scroll the GanttView in its Setter.
2) You could use a BackgroundWorker for the long running loading of the tasks and in its RunWorkerCompleted
event to scroll to the needed time. You could find an example of that in our online demo: http://demos.telerik.com/silverlight/#GanttView/ScrollingPerformance
Hope this helps.
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