Indicates whether this instance of DateTime is within the daylight saving time range for the current time zone.
true if the value of the DateTime.Kind property is DateTimeKind.Local or DateTimeKind.Unspecified and the value of this instance of DateTime is within the daylight saving time range for the local time zone; false if DateTime.Kind is DateTimeKind.Utc.
This method determines whether the current DateTime value falls within the daylight saving time range of the local time zone, which is returned by the TimeZoneInfo.Local property. You can determine whether a time zone supports daylight saving time by retrieving the value of its TimeZoneInfo.SupportsDaylightSavingTime property. For time zones that observe daylight saving time, you can determine when the transition to and from daylight saving time occurs by retrieving the System.TimeZoneInfo.AdjustmentRule array returned by the time zone's TimeZoneInfo.GetAdjustmentRules property.
If the current DateTime value represents either an ambiguous or an invalid time in the local time zone, the method returns false.
On winxp systems, the DateTime.IsDaylightSavingTime method recognizes only the current adjustment rule when determining whether the current instance is a daylight saving time. As a result, the method may not accurately report whether the current instance is a daylight saving time for periods before the current adjustment rule came into effect.