Mask not working with calendar control

I have a textbox with a calendarextender and a maskededitextender.  We use the mask so that user can enter both a date and time in correct format such as xx/xx/xxxx xx:xx AM.  However, when the cursor enters the TextBox and a date is selected from the calendarextender I want it to accept the date and allow entry of a time in hh:mm tt format.  Currently when the date is selected the date goes away and just the mask shows in the TextBox like __/__/____ __:__ AM

Below is the page markup I am using.

<asp:TextBox ID="txtRepairPlanStart" runat="server" 
    Text='<%# Bind("RepairPlanStart", "{0:MM/dd/yyyy hh:mm tt}") %>' onblur="checkmask(this);" /><asp:CalendarExtender ID="CalendarExtender5" runat="server" TargetControlID="txtRepairPlanStart" Format="MM/dd/yyyy"></asp:CalendarExtender><asp:MaskedEditExtender ID="MaskedEditExtender1" runat="server" 
    TargetControlID="txtRepairPlanStart" 
    AcceptAMPM="True" 
    Mask="99/99/9999 99:99" 
    MaskType="DateTime"></asp:MaskedEditExtender>