Thank you for contacting us. I have attached a sample project that demonstrates how you can show the pop-up of radDateTimePicker on button click event. Please, have a look at the code handling for the radButton1_Click event. I hope this is helpful. If you have further issues, do not hesitate to contact us back.
Thany you for the demo application, I have attempted to convert the code with a convertor tool to vb.net without success. Would please either send me a vb version or give me a link to a convertor that will work with the Telerik code.