Removing a duplicate entry & preventing data entry in the cell that had the duplicate.

[FrancisM]

I have a worksheet that is used to make reservations for appointments in 1/5-hour increments. Occasionally a 1-hour slot is required, So, if a hour appointment is made, there is a second entry in these cell ranges B4:C10, B13:C17, E4:E10, E13:E17. I am trying to remove the second entry, & prevent any other entry in these ranges, where the previous entry was located. These are the sheet numbers that don’t need the code to run. "Sheet1", "Sheet11", "Sheet21", "Sheet31", "Sheet41", "Sheet42", "Sheet43", "Sheet44", "Sheet 45", "Sheet46", "Sheet47", "Sheet48", "Sheet49", "Sheet50", "Sheet51", "Sheet52", "Sheet53", "Sheet54", "Sheet55", "Sheet56", "Sheet57", "Sheet82". I have another Private Sub Workbook_SheetChange(ByVal Sh As Object, ByVal Target As Range) code located in Thisworkbook, so I would just add this to that code.
Is what I am asking even possible? I have googled, & have duplicate removal, highlight, & other possibilities, but not what I am asking.

 

[FrancisM]

I have found this code form an earlier post (remove data but keep the Conditional Formatting - 12 April, 2004 - DRJ -Answer).

[COLOR=#333333]Sub Test()[/COLOR]
Dim Cell As Object

    Sheets("Sheet1").Range("A2:T49").FormatConditions.Delete
    For Each Cell In Sheets("Sheet1").Range("A2:T49")
        Select Case Cell.Value
            Case 1 'Color Green
                Cell.Interior.ColorIndex = 10
            Case 2 'Color Red
                Cell.Interior.ColorIndex = 3
            Case Else
        End Select
    Next
     [COLOR=#333333]End Sub
[/COLOR]

I am wondering if it would be possible to use a variation of this code along with the standard conditional formatting of duplicates. The duplicates will be dynamic, & not static.