Quick Start

Use these types for time regardless of location (not caring about leap-seconds):

• UTCTime for actual times
• NominalDiffTime for differences between times, i.e. durations

Use these types for the ways people refer to time and time differences:

• Day for something like June 27th 2017
• DayOfWeek for something like Tuesday
• TimeOfDay for something like 5pm
• LocalTime for a Day with a TimeOfDay
• TimeZone for a time zone offset (not actually the time zone itself) like -0700
• ZonedTime for a LocalTime with a TimeZone
• CalendarDiffDays for something like 6 years, 1 month and 5 days
• CalendarDiffTime for something like 6 years, 1 month, 5 days, 3 hours, 7 minutes and 25.784 seconds

Use this for low-latency timing:

• SystemTime

These are less commonly needed:

• AbsoluteTime and DiffTime if you do care about leap-seconds.
• LeapSecondMap for tracking the leap-seconds
• UniversalTime for time based on Earth rotation