这段代码和你的解释非常混乱。我认为你试图为每一行获取一个月和日的数组，但你的代码是：
1.从单个单元格阅读日期，而不是一行四个单元格。
1.提取该单个日期的日部分;
1.将日期值插入一个名为MonthArray的数组。
如果我没理解错的话，我会这么做：

Sub ParseDates(src As Range)
    Dim dates() As Variant
    dates = src.Value

    Dim rCount As Long
    rCount = src.Rows.Count

    Dim cCount As Long
    cCount = src.Columns.Count

    Dim days() As Variant
    Dim months() As Variant
    Dim dt As Date

    Dim r As Long, c As Long
    For r = 1 To rCount
        For c = 1 To cCount
            dt = CDate(dates(r, c))
            days(r, c) = Day(dt)
            months(r, c) = Month(dt)
        Next c
    Next r

    ... ' Whatever you want to do with your values.
End Sub

浸提天数和月数

Option Explicit

Sub TestR1()
    
    Dim wb As Workbook: Set wb = ThisWorkbook ' workbook containing this code
    
    Dim ws As Worksheet: Set ws = wb.Sheets("Sheet1")
    
    Dim rg As Range
    Set rg = ws.Range("A2", ws.Cells(ws.Rows.Count, "A").End(xlUp))
    Dim rCount As Long: rCount = rg.Rows.Count
    
    Dim Data()
    If rCount = 1 Then
        ReDim Data(1 To 1, 1 To 1): Data(1, 1) = rg.Value
    Else
        Data = rg.Value
    End If
    
    Dim Months() As Long: ReDim Months(1 To rCount)
    Dim Days() As Long: ReDim Days(1 To rCount)
    
    Dim r As Long
    
    For r = 1 To rCount
        Days(r) = Day(Data(r, 1))
        Months(r) = Month(Data(r, 1))
    Next r
    
    Debug.Print "Index", "Day", "Month"
    
    For r = 1 To rCount
        Debug.Print r, Days(r), Months(r)
    Next r
    
    Debug.Print "Max Day", "Max Month"
    Debug.Print Application.Max(Days), Application.Max(Months)

End Sub

立即窗口中的结果（Ctrl+G）

Index         Day           Month
 1             20            4 
 2             16            2 
 3             27            2 
 4             15            3 
 5             26            1 
 6             4             12 
 7             3             2 
 8             26            1 
 9             20            4 
Max Day       Max Month
 27            12