When I do the above with RadControls for ASP.NET AJAX Q1 2011, the times appear in 45 minute intervals, not 15 minute intervals.
If the above code is not included, the time is shown in 3 hour interevals. There seems to be a strange fact of three involved here somewhere! Not sure why anyone would want three hour intervals - I would have though hourly or half-hourly would be more appropriate.
Graham Plowman
Edit: Please remove this message: I realised that the date intervals display across the page instead of down the page.