Both the UNSC and the Covenant use separate, though analogous, measurements to regulate and measure the passage of time and standardise the calendars of their interstellar territories.
“The Military Calendar is the standard timekeeping calendar used by the UNSC and virtually all of...Military Calendar
“The Ross-Ziegler Blip was a stratigraphic event on Earth and a number of other colonized planets...Ross-Ziegler Blip
“A Cycle is a Covenant unit of time. It is one artificial day on High Charity. A cycle contains...Cycle
“Military Standard Time (also called MST) is the official name of the UNSC's 2400 hour...Military Standard Time