RadTimeBar is a content control and not an items control and it has no control over the content that you place in it. I am not sure which control you are using to show your data, but from the provided information, I suppose you should optimize the content control and not the timebar itself. You can easily check this, by removing the content control and testing the timeBar on its own with the same settings - e.g. PeriodStart, PeriodEnd, Intervals collection, etc.
One thing that you should keep in mind, is that RadTimeBar does not virtualize its content - that is, all elements of the content control are created, even the ones that are not currently visible.
Regarding your last question, about drilling down to HourInterval - due to a limitation in Silverlight framework, we have enforced a constraint for zoom-in to maximum of 30 000 pixels. Depending on the period range that the timebar shows, the minimum interval that can be displayed, might be different from the minimum interval that you have added in the Intervals collection. In your case the period range of your timebar is large and when you try to zoom in to a smaller interval, you hit the 30 000 pixel limit.
the Telerik team
Sharpen your .NET Ninja skills
! Attend Q1 webinar week and get a chance to win a license! Book your seat now >>