There isn't a build in event that could be used in the way you explained because there is no proper way to know exactly when the selection really is finished. You could use the KeyUp
event and listen for the Ctrl and Shift keys.
The next code snippet shows the described approach:
sender, KeyEventArgs e)
(e.Key == Key.LeftCtrl || e.Key == Key.RightCtrl || e.Key == Key.LeftShift || e.Key == Key.RightShift)
var calendar = sender
Hole this is helpful.
the Telerik team