Public Gesamt As Date
 
Private Sub cmdAdd_Click()
  If Not IsDate(Text1.Text) Then Exit Sub
  Call Addieren(Text1.Text)
 
  If Not IsDate(Text2.Text) Then Exit Sub
  Call Addieren(Text2.Text)
 
  If Not IsDate(Text3.Text) Then Exit Sub
  Call Addieren(Text3.Text)
 
  If Not IsDate(Text4.Text) Then Exit Sub
  Call Addieren(Text4.Text)
End Sub
 
Private Sub Addieren(Zeit As Date)
  Dim StundeAlt As Integer, MinuteAlt As Integer, SekundeAlt As Integer
  Dim StundeNeu As Integer, MinuteNeu As Integer, SekundeNeu As Integer
 
  StundeAlt = Hour(Gesamt)
  MinuteAlt = Minute(Gesamt)
  SekundeAlt = Second(Gesamt)
 
  StundeNeu = Hour(Zeit)
  MinuteNeu = Minute(Zeit)
  SekundeNeu = Second(Zeit)
 
  Gesamt = TimeSerial(StundeAlt + StundeNeu, _
    MinuteAlt + MinuteNeu, _
    SekundeAlt + SekundeNeu)
 
  Label1.Caption = Gesamt
End Sub

Gruß
Marcus