Thanks for writing.
Currently, in order to change the duration of the transition you need to provide a custom control template which contains your own custom transition. Please have a look at the attached archive. It contains the default control template. You can reuse it and simply replace the transition for RadTransitionControl. Creating your custom transition is pretty straightforward, you just have to inherit from RadTransition and override a few methods. I have also added the code for RadSlideTransition so that you can modify it as required.
Please write again if you need further assistance.
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