Checks whether this instance is equivalent to another. The two instances are considered to be equivalent if any of the following conditions apply: - both instances are type ClockTime. - both instances are type OffsetFromUTC and their offsets from UTC are equal. - both instances are type TimeZone and their time zones are equal. - both instances are UTC. An instance is considered to be UTC if it is either type UTC, or is type OffsetFromUTC with a zero UTC offset.