Today's system of numbering years started with the first year of Entharion's reign as king of Quendor, which marked the start of recorded history (GUE). However, legends and ancient tales lead historians to believe that highly advanced settlements existed on both sides of the Great Sea around the fifth or sixth century Before Entharion (BE or BC), and that humanity began to make its mark on the land as long as two millennia ago.

A year in the Great Underground Empire always has 365 days. This period is divided into twelve months. Each month has a specific number of days in it, except for Frobuary. It is believed that the breakdown of the year into these months might be, in some vague way, related to the lunar cycle, but since the size, shape, and position of the moon is so wildly unpredictable, it is useless to speculate.

The order of the months is like this:
1 Estuary 31
2 Frobuary 28 [35 for Antharian Leap Week]
3 Arch 31
4 Oracle 30
5 Mage 31 [32 with Zero Day]
6 Jam 30
7 Jelly 31
8 Augur 31
9 Suspendur 30
10 Ottobur 31
11 Mumberbur 30
12 Dismembur 31

It should be noted, though, that while the month of Arch always has 31 days, in Antharia, it begins on the seventh day because of Antharian Leap Week.

Frobuary was originally called Fidooshiary until it was purchased by the Frobozz Magic Month Company in 817 GUE.

The average month has a little over four weeks in it. Each week has seven days, known as:
1 Sand Day
2 Mud Day
3 Grues Day
4 Wands Day
5 Birthday
6 Frob Day
7 Star Day

Despite these names, most dates in the Empire are referred to in the standard day number/month/year custom (ex: 14 Mumberbur 883 GUE), but the older style (month/day-number/year; Mumberbur 14'th, 883 GUE) is still used. Putting a comma between the month and the year is optional.

Two of these day names actually have stories behind them:

Frob Day(TR) was purchased by the Frobozz Magic Day Company in 817 GUE.

Birthday originally had a different name, but Dimwit Flathead changed it when he took the throne (c. 770 GUE). Any earlier records to a name before Birthday have been erased. Before the fall of the Empire in 883, Birthday was the official celebration of Dimwit Flathead's birthday. Even after his death Dimwit was excessive, still having his birthday celebrated every week. Dimwit's Birthday is only one of the special holidays that occurs throughout the year.

(see 'holidays' for more information)

SOURCE(S): Zork Zero, Encyclopedia Frobozzica