The switch has an internal clock processor for maintaining correct date, time, and timezone. Typically, the switch ships with a default date and timezone. Then, as part of installing the switch and bringing it online the first time, you set the date, time, and timezone.
-> show /SP/clock datetime timezone
For example, type:
-> show /SP/clock datetime timezone /SP/clock Properties: datetime = Sun Jan 17 20:25:53 2016 timezone = PDT (PST8PDT) ->