Try this code for time entry:
<asp:TextBox ID="txtStartTime" runat="server" Text='<%# Bind("StartTime", "{0:t}") %>' Width="60px"></asp:TextBox>
<asp:Label ID="lblStartTimeEdit" runat="server" Text="Press 'A' or 'P' to switch AM/PM"></asp:Label>
<cc1:MaskedEditExtender ID="meeStartTime" runat="server" AcceptAMPM="true" MaskType="Time" Mask="99:99" MessageValidatorTip="true" OnFocusCssClass="MaskedEditFocus" OnInvalidCssClass="MaskedEditError" ErrorTooltipEnabled="true" UserTimeFormat="None" TargetControlID="txtStartTime" InputDirection="LeftToRight" AcceptNegative="Left">
</cc1:MaskedEditExtender>
<cc1:MaskedEditValidator ID="mevStartTime" runat="server" ControlExtender="meeStartTime" ControlToValidate="txtStartTime" IsValidEmpty="False" EmptyValueMessage="Time is required " InvalidValueMessage="Time is invalid" Display="Dynamic" EmptyValueBlurredText="Time is required " InvalidValueBlurredMessage="Invalid Time"