Currently, it is not possible for this aspect of RadMenu
to be customized. However, we internally use timers just as you have suggested and I added this as a feature request. We will consider exposing an API in one of our upcoming releases. I updated your Telerik points for this suggestion.
Should you have any further questions, do not hesitate to ask.
the Telerik team
Register for the Q2 2011 What's New Webinar Week. Mark your calendar for the week starting July 18th and book your seat for a walk through of all the exciting stuff we will ship with the new release!