From MormonWiki
Most leaders preach punctuality and meetings generally do start on time. However, because
LDS people are busy, many are known to be punctuality impaired. Culturally, this tendency towards tardiness has come to be known as
Mormon Standard Time, a term which is somewhat ridiculously similar to Mountain Standard Time, which is the standard time of
Utah. Mormon Standard Time does not have an exact meaning, but nevertheless, is sometimes taken to mean 15 or 30 minutes after the normal start time of an event (often a church social, or similar activity).