Recently some client of our DNN blog module requested a customized feature, he wanted to out the posted time of SunBlogNuke in a format that included the two letter suffix added to the day number, like "December 25th, 2009" as opposed to "December 25, 2009". After some investigation, it seems this is not supported out of the box (not surprising really). Finally I found the MarkGwilliam’s post (How To Append 'st', 'nd', 'rd' or 'th' To Day Numbers in Dates) which provided a ".NET Framework friendly" to implement this behavior and therefore offers good reuse value and is intuitive for .NET developers to use. I thought that is what we want and then extended it in our customized way which allows SunBlogNuke developers to consume the code more easily and flexible. Now I shared the VB.Net Function below and hope it helps if you also have the similar requirement:

Protected Function FormatPostedTimeWithDayNumberSuffix(Optional ByVal format As String = "MMMM d{0}, yyyy") As String
    Dim dateTime As DateTime = Date.Parse(Entry.PostedTime)
    If Not Null.IsNull(dateTime) Then
        Dim formatTime As String = dateTime.ToString(format)

        Dim day As Integer = dateTime.Day
        Dim dayFormat As String = String.Empty
        Select Case day
            Case 1, 21, 31
                dayFormat = "st"
            Case 2, 22
                dayFormat = "nd"
            Case 3, 23
                dayFormat = "rd"
            Case Else
                dayFormat = "th"
        End Select

        Return String.Format(formatTime, dayFormat)
    End If

    Return Entry.PostedTime
End Function

If you have more better or elegant solution appreciate your comments here. Thanks a lot.