Option Explicit

Private Sub Worksheet_Change(ByVal Target As Range)
Const WS_RANGE As String = "B:B"

   On Error GoTo ws_exit:
   Application.EnableEvents = False
   If Not Intersect(Target, Me.Range(WS_RANGE)) Is Nothing Then
       With Target
           If .Value > 8 Then
               .Offset(0, 1).Value = .Value - 8
               .Value = 8
       End With
   End If

ws_exit:
   Application.EnableEvents = True
End Sub

'This is worksheet event code, which means that it needs to be
'placed in the appropriate worksheet code module, not a standard
'code module. To do this, right-click on the sheet tab, select
'the View Code option from the menu, and paste the code in.

Try this. It may not be the most effecient use of system resources but
it works.

Unfortunately, it fires on EVERY cell that has a number greater than 8,
not just the regular hours.

Code:
--------------------
   Public oldcell As String
 ---------------------
 Private Sub Worksheet_Activate()
 oldcell = ActiveCell.Address
 End Sub
 ---------------------
 Private Sub Worksheet_Change(ByVal Target As Range)
 
 If Range(oldcell).Value > 8 Then
 
 Range(oldcell).Select
 temphrs = ActiveCell - 8
 ActiveCell.Value = 8
 ActiveCell.Offset(0, 1) = ActiveCell.Offset(0, 1) + temphrs
 End If
 oldcell = ActiveCell.Address
 
 
 End Sub
 ---------------------
 Private Sub Worksheet_SelectionChange(ByVal Target As Range)
 oldcell = ActiveCell.Address
 
 End Sub
--------------------