The polities descended from the Republic of Is do not use days, weeks, or other terrestrial dating systems other than for historical or archaeological purposes; however, the classical second has been retained as the basis of timekeeping.
Here's a quick ready-reckoner:
one second
One second, the time taken for light to travel 299,792,458 meters in vacuum
one kilosecond
Archaic: 16 minutes
one hundred kiloseconds (1 diurn)
Archaic: 27 hours, 1 day and three hours
one megasecond (1 cycle)
Ten diurns. Archaic: eleven days and six hours
thirty megaseconds (1 m-year)
300 diurns. Archaic: 337 Earth days (11 months)
one gigasecond
Archaic: approximately 31 Earth years
one terasecond
Archaic: approximately 31,000 Earth years (half age of human species)
one petasecond
Archaic: approximately 31,000,000 Earth years (half elapsed time since end of Cretaceous era)