Quelle heure avez-vous ?

Private Sub CommandButton1_Click()
TextBox3 = SommeHeures(TextBox1, "-" & TextBox2) 'soustraction
End Sub

Function SommeHeures(h1, h2)
Dim signe1%, signe2%, s
On Error Resume Next
If Not h1 Like "*:*:*" Then h1 = h1 & ":0" 'secondes manquantes
If Not h2 Like "*:*:*" Then h2 = h2 & ":0"
signe1 = IIf(Left(h1, 1) = "-", -1, 1)
signe2 = IIf(Left(h2, 1) = "-", -1, 1)
s = Split(Replace(h1, "-", ""), ":")
h1 = signe1 * (s(0) / 24 + s(1) / 1440 + s(2) / 86400)
s = Split(Replace(h2, "-", ""), ":")
h2 = signe2 * (s(0) / 24 + s(1) / 1440 + s(2) / 86400)
s(0) = Int(CDec(24 * Abs((h1 + h2))))
s(1) = Format(Minute(Abs(h1 + h2)), "00")
s(2) = Format(Second(Abs(h1 + h2)), "00")
SommeHeures = IIf(h1 + h2 < 0, "-", "") & Join(s, ":")
If Err Then SommeHeures = "" 'facultatif...
End Function

TextBox4 = SommeHeures(SommeHeures(TextBox1, "-" & TextBox2), "-" & TextBox3)