Hello Roger Andersson,
An all day appointment is an appointment with start time: 12:00 AM and end time: 12:00 PM.
So to be able to have the entire appointment as "all day" from 2010-01-21 to 2010-01-23 you only have to select the dates and then check the "All Day" checkbox:
Please let me know if you have further questions.
the Telerik team
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