There is already a feature in the IOS that will allow you set to whatever PDT is set in your location. See below. The feature below allows you to set the start and end of daylight saving time according to your parameters, it can be done a one time with "recurring" keyword.
router(config)#clock summer-time PDT recurring ?
<1-4> Week number to start
first First week of the month
last Last week of the month
router(config)#clock summer-time PDT recurring 2 ?
DAY Weekday to start
router(config)#clock summer-time PDT recurring 2 Sunday ?
MONTH Month to start
router(config)#clock summer-time PDT recurring 2 Sunday march ?
hh:mm Time to start (hh:mm)
router(config)#clock summer-time PDT recurring 2 Sunday march 02:00 ?
<1-4> Week number to end
first First week of the month
last Last week of the month
router(config)#clock summer-time PDT recurring 2 Sunday march 02:00 1 sunday november 02:00
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