Please review the following help article
that elaborates on showing/hiding controls with ajax. The hidden controls should be nested in always visible container and this container added to the AjaxSettings instead. In this line of thoughts, table rows cannot be updated with ajax as it breaks its structure. You can either use the table cells or the entire table. Then locate the controls in PreRender and add them to the AjaxSettings:
protected void rptTest_PreRender(object sender, System.EventArgs e)
foreach ( item in rptTest.Items)
RadTimePicker rtp1 = item.FindControl("RadTimePicker1");
RadTimePicker rtp2 = item.FindControl("RadTimePicker2");
Hope this helps.
the Telerik team