RadNumericUpDown exposes Delay
properties that can be used to control this behavior. The default value for both is250 ms. To achieve what you want, just reduce the value of the Delay
property to 100ms (for example) or any value that suits your scenario and maybe increase the RepeatInterval
a litle bit . I am sure that if you adjust this two properties you will be able to get what you need. Keep in mind that this properties affect only keyboard arrows not clicking on up/down buttons or mouse scrolling.
Let me know if you need more help.
the Telerik team