The Gantt widget always stores tasks in UTC as there is no timezones support implement yet. This means that Gantt will always assume the entered date on the client is in UTC and the server-side storage is UTC as well. In general, this approach should work just fine in the majority of the cases.
In case this does not fit your scenario would you please describe the use case? In general we have a timezones feature planned, which will add the possibility to save a task in a given time zone (in your case this would be PST).
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