Option Explicit 
Sub Date_Finder() 
     
    Dim Wb As Workbook 
    Dim Ws As Worksheet 
    Dim LookVal, MaxDate, MinDate, CloseDate, x, y As Double 
    Dim LastRow, i As Long 
    Dim Rng, c As Range 
    Dim DateArray() As Variant 
     
     'You can change Workbook or Worksheet
     'where value will be looked for
    Set Wb = ActiveWorkbook 
    Set Ws = Wb.Worksheets("Date") 
     
    With Ws 
         'You can change column letter where match can be found
         'and change 1 to 2 if you have a header
        LastRow = .Range("B65536").End(xlUp).Row 
        Set Rng = .Range("B1:B" & LastRow) 
         
         'You can change reference to the cell which will be
         'used to find the match
        LookVal = CDbl(.Range("A1").Value) 
         
    End With 
     
     'Looking for Max and Min date within the renge
    MaxDate = WorksheetFunction.Max(Rng) 
    MinDate = WorksheetFunction.Min(Rng) 
     
     'Declaring an Array
    ReDim DateArray(1 To LastRow) 
     
    If LookVal < MaxDate Then 
        If LookVal > MinDate Then 
             
            For Each c In Rng 
                i = i + 1 
                 'This will create an Array with differences
                 'beetween looked value and values within the range
                DateArray(i) = Abs(DateDiff("d", CDbl(c), LookVal)) 
            Next c 
             
             'This will give you 2 the closest values
            CloseDate = WorksheetFunction.Min(DateArray()) 
            x = LookVal + CloseDate 
            y = LookVal - CloseDate 
             
             'This will set up conditional formating to highlight all the
             'cells with matching values
            With Rng 
                .FormatConditions.Delete 
                .FormatConditions.Add Type:=xlCellValue, Operator:=xlEqual, _ 
                Formula1:=x 
                 'You can change colour index here
                .FormatConditions(1).Interior.ColorIndex = 3 
                .FormatConditions.Add Type:=xlCellValue, Operator:=xlEqual, _ 
                Formula1:=y 
                .FormatConditions(2).Interior.ColorIndex = 3 
            End With 
        Else 
             'This will set up conditional formating to highlight all the
             'cells with matching values
            With Rng 
                .FormatConditions.Delete 
                .FormatConditions.Add Type:=xlCellValue, Operator:=xlEqual, _ 
                Formula1:=MinDate 
                .FormatConditions(1).Interior.ColorIndex = 3 
            End With 
        End If 
    Else 
         'This will set up conditional formating to highlight all the
         'cells with matching values
        With Rng 
            .FormatConditions.Delete 
            .FormatConditions.Add Type:=xlCellValue, Operator:=xlEqual, _ 
            Formula1:=MaxDate 
            .FormatConditions(1).Interior.ColorIndex = 3 
        End With 
    End If 
End Sub