AnimationDuration defines the length of the slide animation in milliseconds. Setting AnimationDuration to a value larger than 0, will cause the drag slider and selected region to be updated using a linear animationBy default AnimationDuration value is 100 (ms). To disable slide animation set AnimationDuration to 0.
<telerik:radslider id="RadSlider1" runat="server" AnimationDuration="500" />
RadSlider1.AnimationDuration = 500;
RadSlider1.AnimationDuration = 500