How To Copy a File One Time, Two Days After it was Created…

Hi,
I'm trying to make a backup of a file, two days after it was created by me, but ONLY if it hasn't been modified in the meantime.
The scenario:
I create a payroll spreadsheet and upload it to Dropbox. A colleague references that spreadsheet the next day, but makes no changes to it. The following day, I would like that spreadsheet to get copied to my backup folder. I can't figure out how to make that happen. "Date Last Opened" → Is After → "Date Created" gets me close, but it's not specific enough.
I already have a rule that if my colleague makes changes, it copies that to my backup folder after the spreadsheet is saved. I don't want to create a copy prior to my colleague's use of the spreadsheet because I never know if she's going to modify it, and then I end up with two copies. I only want the "final" copy saved in my backups.
Thank you in advance for any help!
I'm trying to make a backup of a file, two days after it was created by me, but ONLY if it hasn't been modified in the meantime.
The scenario:
I create a payroll spreadsheet and upload it to Dropbox. A colleague references that spreadsheet the next day, but makes no changes to it. The following day, I would like that spreadsheet to get copied to my backup folder. I can't figure out how to make that happen. "Date Last Opened" → Is After → "Date Created" gets me close, but it's not specific enough.
I already have a rule that if my colleague makes changes, it copies that to my backup folder after the spreadsheet is saved. I don't want to create a copy prior to my colleague's use of the spreadsheet because I never know if she's going to modify it, and then I end up with two copies. I only want the "final" copy saved in my backups.
Thank you in advance for any help!