Format to open file based on Date Modified stamp

What is the proper format to specify a file to include the date modified? Example: How would I open the file called "Scooters.xlsx" with the date modified being 8/23/2011 2:03 PM?

The reason is that I want to specify the file names available through a drop down, but want to make sure that it opens the EXACT file, not one that has been modified and saved with the same name but with a different modified date. So if someone edits the original file and saves it, the main workbook will error out because the exact file name and modified date will be incorrect.

I have everything already done and it opens the files based on the name, I just want to specify the date modified as well.

Thank you