As these buttons are nothing more than standard MS RepeatButtons, you can modify their Delay and Interval properties to suit your requirements. To do so, you have to modify the DocumentHostTemplate of the RadPaneGroup(s). You can have a look at the Editing Control Templates article for more information.
For your convenience, I'm attaching a sample project where I've set the Delay and Interval properties for the buttons to 0. Of course, you can further modify these values to your liking.
I hope you find this helpful. If I can be of any further assistance, please let me know.
Regards,
Dilyan Traykov
Progress Telerik
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