Check this solution from exceluser.com:
Public Function LastSaveTime() As String
Application.Volatile
LastSaveTime = ThisWorkbook.BuiltinDocumentProperties("Last Save Time")
End Function
This should also work with a Workbook which is stored in a sharepoint library - just tested it with SharePoint 2010
Edit to grab data from SharePoint List:
Check this Link - there it is explained how you are able to read list data into excel.
With this Link you will be able to get the ListName and the ViewName.
With those 2 combined the easiest way would be to create a new view for the list and add only the change column to the view - when the data has been imported to excel you can read that data easily and drop the added table again.
Hope this helps to get you in the right direction. (Tested and working with SP2010 List)