The 5 laws of API dates and times

Repost from APIUX.com: http://apiux.com/2013/03/20/5-laws-api-dates-and-times/

In short:

Law #1: Use ISO-8601 for your dates
Law #2: Accept any timezone
Law #3: Store it in UTC
Law #4: Return it in UTC
Law #5: Don’t use time if you don’t need it