Open the DropDown When the Control Gets Focus
RadDateTimePicker's API gives you the ability to open the DropDown when the control gets focus. In order to enable this behavior, you should set the RadDateTimePicker's OpenDropDownOnFocus property to True.
Example 1: Set the OpenDropDownOnFocus property
<telerik:RadDateTimePicker OpenDropDownOnFocus="True"/>
The default value of the RadDateTimePicker's OpenDropDownOnFocus property is False.