How do I create a custom global function? (for time zone conversion)

Domenick 

You can add a custom column in PowerQuery to adjust the UTC back like this.

[Date] + #duration(0,-8,0,0)

I solved this by adding a Custom Column in Query Editor which brings the time in as UTC and converts it to PST or PDT based appropriately. The -7 and the -8 are the offset hours (Pacific time is either 7 or 8 hours behind UTC depending on the time of year). I strung this solution together with the help of this guidance by Rickmaurinus : https://gorilla.bi/power-query/last-refresh-datetime/  

let
UTC_DateTimeZone = DateTimeZone.UtcNow(),
UTC_Date = Date.From(UTC_DateTimeZone),
StartSummerTime = Date.StartOfWeek(#date(Date.Year(UTC_Date), 3, 31), Day.Sunday),
StartWinterTime = Date.StartOfWeek(#date(Date.Year(UTC_Date), 10, 31), Day.Sunday),
UTC_Offset = if UTC_Date >= StartSummerTime and UTC_Date < StartWinterTime then -7 else -8,
PST_Timezone = DateTimeZone.SwitchZone(UTC_DateTimeZone, UTC_Offset)
in
PST_Timezone