converting data reported in prevailing time to standard time

I have multiple years worth of hourly data that i pull from my data provider. they report data in pacific prevailing time. i would like to be able to convert this to pacific standard time. what is the best way to accomplish this so that i am always pulling 8760 values for each calendar year (ignoring leap year). i have a data table that does the mapping between standard timezone and prevailing timezone but when i try to connect the data tables i run into a many-to-many relationship issue.