Timestamp formatting

I have a database of manufacturing data that I have multiple methods of pulling data from. These different methods are not interchangeable and need to be used at different times. One method exports as .csv, and another method exports as .xls. The problem I am having is with the formatting of the timestamps of the .xls worksheet. In the .xls, the timestamp is exported in a format that is not recognized by excel (as shown when trying to sort, it will say A to Z instead of Oldest to Newest). However, by simply clicking in the cell and hitting enter, I can change the cell into a format that excel recognizes as a time. This is not feasible for 40,000+ points per day. Does anyone have any ideas as to how I could quickly reformat the whole column? Highlighting the whole column and using the number tab does not work correctly.Example.xlsx