Post History

Your time travelers are not being smart.

Instead of bringing loot back with them, they should bury it in a place that they know they will have private access to in the present, and where nobody thought of digging.  Then they can uncover the artifacts when they get back.  The loot will pass all carbon dating and other tests since it really is old.

Your time travelers could even include tablets with inscriptions linking the artifacts to a particular king, artisan, or whatever, complete with intriguing story of why they were buried there.

The time travelers would certainly see things modern historians don't know about.  The tablets could provide pointers to other locations to dig, what modern archeologists would find there, and some useful but currently unknown historical context.  That would help validate the rest of the cache found with the tablets as not just being something you buried and very skillfully made appear old.

One problem with all this could be antiquity laws.  Some governments view ancient artifacts as public property, whether found on private land or not.  I don't know what the laws are in modern Egypt, but they are probably a reaction to foreigners essentially looting the place and carting off lots of treasures until only recently.  The government may take the found loot, with maybe only modest compensation to the finders.

One possible way around the above is to leave the loot in a "shipwreck" in what is today international waters.  You have to be  careful to pick a place someone wouldn't notice a sonar anomaly and investigate before you could "discover" the wreck yourself.