Or just go to a big box retailer, grab a couple of serial numbers off of the packaging, and then randomize per page.
Except if you can manipulate the timestamps, then they aren't relevant anymore, so the search space is much bigger than the intersection of each set of days.
It's the intersection of all the people who visited each printer at least once any time.
If everything you print has the same fictitious serial number, it's still a stable identifier that can be triangulated.