Same day(s) different(s) hour(s) in a excel schedule

[milt2010]

Hello!
I am creating a schedule and have a problem with duplicate hours.
The scenario is the following:
in a column (A) I enter the date of the day; in another (B) the start time and in the following (C) the end time. What I would like is that the same start and end times cannot be entered on the same dates.

Examples:

Wrong scenario

Right scenario

Is it possible to achieve this, using the data validation tool with a formula?
Thanks in advance.

 

[Logit]

Sub DupRws()

    Application.ScreenUpdating = False

    Dim sFormula As String
    Dim rRng As Range
    Dim nCol As Integer, i As Integer

    Set rRng = Range("A1").CurrentRegion
    nCol = rRng.Columns.Count
    Range("A1").Select
    
    'build the formula
    sFormula = "=COUNTIFS("

    For i = 1 To nCol
      sFormula = sFormula & rRng.Columns(i).Address & "," & _
         rRng.Cells(1, i).Address(False, True)
      If i < nCol Then sFormula = sFormula & ","
    Next
    sFormula = sFormula & ")>1"

    'write the formula in helper cell to get it's local version
    rRng.Cells(1, nCol + 1).Formula = sFormula

    rRng.FormatConditions.Delete
    With rRng.FormatConditions.Add(Type:=xlExpression, _
            Formula1:=rRng.Cells(1, nCol + 1).FormulaLocal)
       .Interior.ThemeColor = xlThemeColorAccent3
    End With

    rRng.Cells(1, nCol + 1).Clear

    Application.ScreenUpdating = True
End Sub

 

[milt2010]

Thanks for your answer ... Unfortunately, I'm not very familiar with VBA. So, I copied and pasted the code into the VBA editor, but it doesn't seem to work

 

[milt2010]

Can anyone else help?...