The Imperial CalendarThe standard Imperial calendar is 365 standard days of 24 standard hours each. For the purposes of this campaign, it was further divided into 13 cycles (months) of 28 days - using Greek lettering Alpha through Nu. The first day of the year - Emperor's Day - does not belong to any cycle (but is listed on Cycle Alpha for convenience).
Imperial dates are written in the format of day-year, where the day is three digits and the year being the Imperial Year. Thus, 001-1105 is Emperor's Day in the Imperial Year One-thousand, One-hundred and Five since the founding of the Third Imperium.
Informally, each cycle is broken into four weeks of seven days each. Each day of the week has a name for clarity, though these are generally used only for convenience for residents of worlds who don't travel much. The week starts on Uniday, and is followed by Biday, Triday, Tetraday, Pentday, Hexaday and Septday.
On most worlds, the local days don't match up with the Imperial Calendar days. For the residents, they use whatever local timekeeping system that works best for them. Travellers tend to stick to the regularity of Imperial timekeeping, relying on pocket computers and advanced chronometers to make conversions to local time, when needed. Because of this, starports operate on Imperial time rather than local. Thus, on a slowly rotating or face-locked world, more than one Imperial day may elapse before a planetary one. Travellers will simply refer to whatever Imperial day the sun rises as being that for the whole "planetary day" and skipping whatever days elapse before the next sunrise.
Starship owners typically set up their ship mortgages so that there are 12 payments per year. That leaves one cycle each year without a payment to allow for annual maintenance costs and lost revenue without additional financial hardship. Holders of such mortgages often send a report of their activities for the previous year to the financial institution that issued the loan during this designated cycle. If any nobles issued a letter of credit on behalf of the owner, they are usually sent a copy of that letter as well.
The Imperial Calendar (Perpetual)
001 Emperor's Day
002 - 029 Cycle Alpha
030 - 057 Cycle Beta
058 - 085 Cycle Gamma
086 - 113 Cycle Delta
114 - 141 Cycle Epsilon
142 - 169 Cycle Zeta
170 - 197 Cycle Eta
198 - 225 Cycle Theta
226 - 253 Cycle Iota
254 - 281 Cycle Kappa
282 - 309 Cycle Lambda
310 - 337 Cycle Mu
338 - 365 Cycle Nu
Despite all the years and campaigns of Traveller I have run, it always amazes me how quickly time passes in the game universe. In the current campaign (as of this writing), over a year and a half of game time has passed in just 16 game sessions!