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The information you want is shown in the document properties (File > Properties in earlier versions of Excel / Info > Properties in Excel 365). There you will find the dates "Created" and "Last modified". You can also access the properties by right-clicking on a file name in Windows Explorer. In fact, in that presentation you get more information, such as who created or last modified the file.
The Created date is the date (and time) when the file was created. In your system that would be when the copy was made but not when you first started the file. The Last Modified date (and time) is any time after the creation when a change was made and the file saved. I find that the properties don't fully replace a system of renaming files with a date. Therefore I still rename my own files with a date. But as a backup as you wish for this should work perfectly.