Display Date with Time in TextBox on calendar selection changed event using C# in ASP.Net

Hi! I have calendar, textbox and gridview in form. When I click calendar then show date in textbox(19.10.2016). But I want show date and time in textbox. I get date from calendar and time from gridview it’s worked correct some computer and incorrect some computer. After click gridview it’s show this. 19/10.2016 16.09. I want always show this format 19.10.2016 16.10.

<script src="Scripts/jquery-1.8.3.min.js" type="text/javascript"></script>
<script type="text/javascript">
    $(function () {
        $("[id*=Grid] td").bind("click", function () {
            var date = $('[id*=hfsana]').val();
            $('[id*=Tbox]').val(date + ' ' + $(this).html());
        });
        return false;
    });
    </script>
<script type="text/javascript">
    $(function () {
        var th = $('[title="Calendar"]').find('tr').eq(2).find('th');
        $(th)[0].innerHTML = 'Як'; // SunDay
        $(th)[1].innerHTML = 'Дш'; // MonDay
        $(th)[2].innerHTML = 'Сш'; // TuesDay
        $(th)[3].innerHTML = 'Чш'; // WednesDay
        $(th)[4].innerHTML = 'Пш'; // ThursDay
        $(th)[5].innerHTML = 'Ҷм'; // Friday
        $(th)[6].innerHTML = 'Шб'; // Saturday
    });
</script>

<asp:Calendar ID="Calendar" runat="server" 
            onselectionchanged="Calendar_SelectionChanged">            
    </asp:Calendar>

protected void Calendar_SelectionChanged(object sender, EventArgs e)
        {
            DateTime dt = new DateTime();
            dt = Convert.ToDateTime(DateTime.Now.ToShortDateString());
            DateTime dat = new DateTime();
            dat = Convert.ToDateTime(Calendar.SelectedDate.ToShortDateString());
            if (dat >= dt)
            {
                Tbox.Text = dat.ToString("dd.MM.yyyy");
            }
            else
            {
                Page.ClientScript.RegisterStartupScript(this.GetType(), "ErrorAlert", "alert('Санаи гузашта интихоб карда намешавад!!!');", true);
                Tbox.Text = "";
            }
            if (dat.ToShortDateString().Length == 4)
            {
                data = dat.ToShortDateString();// +"0" + dat.ToShortDateString();
                hfsana.Value = dat.ToShortDateString();
            }
            else
            {
                data = dat.ToShortDateString();
                hfsana.Value = dat.ToShortDateString();
            }
}