It is 16 different types of sands of sosaria, each having a unique hue, containing a brief history of the respective year from 1997 to 2012.
For the Britannian date, we can see in the game that five seconds is a minute in Britannia, which makes the time 12 times faster. The first four items on
UO Stratics - Time are according to that fact:
However, as far as I can understand, at one point, someone calculated "One Earth year equals five Britannian years" according to some type of a source which I have no idea of today. In order to adapt the date to this new information while maintaining the fact that the time passes 12 times faster, they had to make a Britannian year 12/5 times longer. Thus, a Britannia year became 365 * 12 / 5 = 876 days and a Britannia month became 876 / 12 = 73 days. This is where that magic number, "73", comes from on the last four items of the same page:
