Imports System
  Namespace myApps
    Public Class DateDiff
      Public Sub DateDiff()
        'costruttore di default
      End Sub
      Public Enum howToCompare
        m = 1
        s
        t
        mm
        yyyy
        q
        d
      End Enum
      Public Shared Function GetDiff(ByVal mode As howToCompare, ByVal startDate As System.DateTime, ByVal endDate As System.DateTime) As Double
        Dim diff As Double = 0
        Try
          Dim ts As System.TimeSpan = New System.TimeSpan(startDate.Ticks - endDate.Ticks)
          Select Case (mode.ToString().ToLower())
            Case "m"
              diff = Convert.ToDouble(ts.TotalMinutes)
              Exit Select
            Case "s"
              diff = Convert.ToDouble(ts.TotalSeconds)
              Exit Select
            Case "t"
              diff = Convert.ToDouble(ts.Ticks)
              Exit Select
            Case "mm"
              diff = Convert.ToDouble(ts.TotalMilliseconds)
              Exit Select
            Case "yyyy"
              diff = Convert.ToDouble(ts.TotalDays / 365)
              Exit Select
            Case "q"
              diff = Convert.ToDouble((ts.TotalDays / 365) / 4)
              Exit Select
            Case Else 'd
              diff = Convert.ToDouble(ts.TotalDays)
              Exit Select
          End Select
      Catch
        diff = -1
      End Try
      Return diff
    End Function
  End Class
End Namespace

Un esempio di utilizzo

<%@ Page language="vb" %>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN" >
<HTML>
<HEAD>
<script runat="server">
Private Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs)
  Dim oggi As DateTime = DateTime.Now
  Dim domani As DateTime = oggi.AddDays(1)
  Dim diff As Double = _
  myApps.DateDiff.GetDiff(myApps.DateDiff.howToCompare.m, domani, oggi)
  Response.Write(diff.ToString())
End Sub
</script>
</HEAD>
<body>
<form id="Form1" method="post" runat="server">
</form>
</body>
</HTML>

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