National Treasure Wiki
$100 bill
Found Patrick's money, brought to Philadelphia
Leads to Ocular Device
Found by Benjamin Franklin Gates

Ben looking at the back of the bill.

While in Philadelphia, Ben saw an engraving of 2:22 pm on the back of a $100 bill. Ben and Abigail think they had missed the time, it was 3:22, but Riley Poole tells them that they still have time to see where the next clue is. This was because of daylight saving. Daylight savings didn't come around till WWI, so 3:22 now would be 2:22 in the 1700s.

Fact*: On the back of the $100 bill, there is an etching of Independence Hall, and the time on the clock tower reads 2:22. The clock on the back of the early-2000s $100 bill (below) was officially documented as reading 4:10, though it does look more like the hour hand is pointing to the two, suggesting a time of 2:22.

newer bills with the blue hologram strip have the time as 10:30.