Dim time1 As String = "12.6.2012 17:50:00"
Dim time2 As String = "12.6.2012 14:25:20"
 
Dim dt1 As Date, dt2 As Date
 
If Date.TryParse(time1, dt1) AndAlso Date.TryParse(time2, dt2) Then
   Dim ts As TimeSpan = dt1 - dt2
   MsgBox(ts.TotalSeconds.ToString & " Sekunden")
End If

TextBox3.Text = (CDate(TextBox2.Text) - CDate( _
  TextBox1.Text)).TotalMinutes.ToString()

Option Strict On
Option Explicit On
 
Public Class TimeSpan_Demo
    Inherits System.Windows.Forms.Form
 
 
    Dim lblstart As New Label With _
        {.Parent = Me, .Top = 20, .Width = 100, .Text = "Startzeit: "}
    Dim tboStart As New TextBox With _
        {.Parent = Me, .Top = 20, .Width = 100, .Left = 110}
 
    Dim lblEnde As New Label With _
        {.Parent = Me, .Top = 50, .Width = 100, .Text = "Endzeit: "}
    Dim tboEnde As New TextBox With _
        {.Parent = Me, .Top = 50, .Width = 100, .Left = 110}
 
    Dim WithEvents btnZeitspanne As New Button With _
        {.Parent = Me, .Top = 80, .Width = 200, _
         .Text = "Zeitintervall berechnen"}
 
 
    Private Sub btnZeitspanne_Click _
        (sender As Object, e As System.EventArgs) Handles btnZeitspanne.Click
 
        Dim start, ende As Date
        If Not Date.TryParse(tboStart.Text, start) Then
            MsgBox("Ungültige Startzeit") : Exit Sub
        End If
 
        If Not Date.TryParse(tboEnde.Text, ende) Then
            MsgBox("Ungültige Endzeit") : Exit Sub
        End If
 
        'Die Zeitachse arbeitet mit der Einheit Ticks
        'Berechnung des Intervalls
        Dim ts As New TimeSpan(ende.Ticks - start.Ticks)
 
        If ts.Ticks < 0 Then
            MsgBox("Start liegt später als Ende") : Exit Sub
        End If
 
        MsgBox("Die Zeitspanne beträgt " & _
          ts.TotalMinutes.ToString("0.##") & " Minuten")
 
        'In eine Textbox würde man das so eintragen
        'Textbox3.Text = ts.totalminutes.tostring("0.##")
 
        'Faktor
        'Textbox4.Text = (ts.totalminutes * 7).tostring("0.##")
 
    End Sub
 
 
    Private Sub TimeSpan_Demo_Load(sender As System.Object, _
        e As System.EventArgs) Handles MyBase.Load
 
        Me.FormBorderStyle = Windows.Forms.FormBorderStyle.FixedSingle
        Me.Size = New Size(300, 200)
 
    End Sub
 
 
    Private Sub InitializeComponent()
        Me.SuspendLayout()
        '
        'TimeSpan_Demo
        '
        Me.ClientSize = New System.Drawing.Size(292, 273)
        Me.Name = "TimeSpan_Demo"
        Me.ResumeLayout(False)
 
    End Sub
End Class