夏时制开始时，时钟时间将按此属性中指定的时间长度向前调整。

At the start of daylight saving time, the clock time is advanced by the length of time specified in this property.

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如果此值为负值，则时钟时间会在夏时制开始时向后调整，而在夏时制结束时向前调整。

If this value is negative, the clock time is set back at the start of daylight saving time and advanced at the end.

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比如说，美国最近将夏时制的开始时间推后了，这样现在已经进入了美国的夏时制而尚未进入欧洲的夏时制。

For example, the United States recently brought back the start of their Summer time, so now it's Summer time in the United States but not Summer time in Europe.

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