Show count down timer using C# and VB.Net in ASP.Net

Hi nauna,

I have created sample code which fulfill your requirement.

HTML

<div>
    <asp:ScriptManager ID="ScriptManager1" runat="server" />
    <asp:UpdatePanel runat="server">
        <ContentTemplate>
            <asp:Label ID="lblTime" Text="text" runat="server" />
            <asp:Timer ID="timer" runat="server" Interval="1000">
            </asp:Timer>
        </ContentTemplate>
    </asp:UpdatePanel>
</div>

C#

protected void Page_Load(object sender, EventArgs e)
{
    DataTable dt = new DataTable();
    dt.Columns.Add("EndDate", typeof(DateTime));
    dt.Rows.Add("2017-03-08 17:00:34.943");
    DateTime startDate = DateTime.Now;
    DateTime endDate = Convert.ToDateTime(dt.Rows[0]["EndDate"].ToString());
    lblTime.Text = CalculateTimeDifference(startDate, endDate);
}

public string CalculateTimeDifference(DateTime startDate, DateTime endDate)
{
    int days = 0; int hours = 0; int mins = 0; int secs = 0;
    string final = string.Empty;
    if (endDate > startDate)
    {
        days = (endDate - startDate).Days;
        hours = (endDate - startDate).Hours;
        mins = (endDate - startDate).Minutes;
        secs = (endDate - startDate).Seconds;
        final = string.Format("{0} days {1} hours {2} mins {3} secs", days, hours, mins, secs);
    }
    return final;
}

VB.Net

Protected Sub Page_Load(sender As Object, e As EventArgs)
	Dim dt As New DataTable()
	dt.Columns.Add("EndDate", GetType(DateTime))
	dt.Rows.Add("2017-03-08 17:00:34.943")
	Dim startDate As DateTime = DateTime.Now
	Dim endDate As DateTime = Convert.ToDateTime(dt.Rows(0)("EndDate").ToString())
	lblTime.Text = CalculateTimeDifference(startDate, endDate)
End Sub

Public Function CalculateTimeDifference(startDate As DateTime, endDate As DateTime) As String
	Dim days As Integer = 0
	Dim hours As Integer = 0
	Dim mins As Integer = 0
	Dim secs As Integer = 0
	Dim final As String = String.Empty
	If endDate > startDate Then
		days = (endDate - startDate).Days
		hours = (endDate - startDate).Hours
		mins = (endDate - startDate).Minutes
		secs = (endDate - startDate).Seconds
		final = String.Format("{0} days {1} hours {2} mins {3} secs", days, hours, mins, secs)
	End If
	Return final
End Function

Screenshot