Although there is no "AJAX Timer" control in the ASP.NET AJAX suite opposite to the "Classic" RadAjax for ASP.NET, the "Classic" RadAjaxTimer still can be used with the new RadAjax framework.
The example here illustrates how to AJAXify the standard MS Timer control with RadAjaxManager. There is a bit tricky part here -- one cannot add the Timer control directly to the AJAX settings as updated control. Instead, just wrap the timer in a container like ASP:Panel and set the container as updated control.
The example also demonstrates continuous update of RadGrid per certain interval. This however can be achieved by binding the Grid client or server-side through Web Service. See demos in the Related Resources tab.