Program to convert time in seconds to hh:mm:ss format

I am trying to make a simple program to convert time given in seconds to hh:mm:ss format. But for some particular input values it produces an incorrect time format. This is what I have tried:

Public Class Form1
    Dim Hours, Minutes, Seconds As Integer

    Private Sub btnReset_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnReset.Click
        lblHours.Text = "00"
        lblMinutes.Text = "00"
        lblSeconds.Text = "00"
        txtTimeSeconds.Text = ""
        txtFormattedTime.Text = ""
    End Sub

    Private Sub btnCalculate_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnCalculate1.Click
        Seconds = Integer.Parse(txtTimeSeconds.Text)
        Hours = Seconds / 3600
        Seconds = Seconds Mod 3600
        Minutes = Seconds / 60
        Seconds = Seconds Mod 60

        lblHours.Text = Hours.ToString.PadLeft(2, "0"c)
        lblMinutes.Text = Minutes.ToString.PadLeft(2, "0"c)
        lblSeconds.Text = Seconds.ToString.PadLeft(2, "0"c)

        txtFormattedTime.Text = Hours.ToString.PadLeft(2, "0"c) & ":" & Minutes.ToString.PadLeft(2, "0"c) & ":" & Seconds.ToString.PadLeft(2, "0"c)
    End Sub
End Class

It works when the input value is 30:

It does not work when the input value is 31:

What have I done wrong? How can I fix this problem?

There is class in .NET called TimeSpan which makes your code easy and elegant.

Example:

dim iSecond as double = 0 'Total number of seconds
Dim iSpan As TimeSpan = TimeSpan.FromSeconds(iSecond)

lblHours.Text = iSpan.Hours.ToString.PadLeft(2, "0"c)
lblMinutes.Text = iSpan.Minutes.ToString.PadLeft(2, "0"c)
lblSeconds.Text = iSpan.Seconds.ToString.PadLeft(2, "0"c)

txtFormattedTime.Text = iSpan.Hours.ToString.PadLeft(2, "0"c) & ":" & _
                        iSpan.Minutes.ToString.PadLeft(2, "0"c) & ":" & _
                        iSpan.Seconds.ToString.PadLeft(2, "0"c)