For the appointment which have a very small duration, it is expected to be rendered as elements with small height. You could take a look at the online demo, and see how the EnableExactTimeRendering property is used: RadScheduler: Exact Time Rendering
Could you please explain a little bit more about the scenario you are trying to achieve? Also, you could open a support ticket, and send us a sample project with the issues isolated in it, so we will be able to troubleshoot this behavior locally.
the Telerik team
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