Increase decrease time with a spin button

Hi all,

I am trying to create code to increase and decrease the time using a spin button. I am unsure how to do this. I have the following code to increase and decrease date but i am unsure how to do it for the time. Any help is much appreciated?

Private Sub UserForm_Initialize()
Reg17.Text = Format(Date, "dd/mm/yyyy")
End Sub

Private Sub spInviteAtt_SpinDown()
Reg17.Text = Format(CDate(Reg17.Text) - CDate(spInviteAtt.SmallChange), "dd/mm/yyyy")
End Sub

Private Sub spInviteAtt_SpinUp()
Reg17.Text = Format(CDate(Reg17.Text) + CDate(spInviteAtt.SmallChange), "dd/mm/yyyy")
End Sub