getOffset
Determines the offset to UTC in effect during a particular @interval of time in the time zone @tz.
The offset is the number of seconds that you add to UTC time to arrive at local time for @tz (ie: negative numbers for time zones west of GMT, positive numbers for east).
Return
the number of seconds that should be added to UTC to get the local time in @tz
Since
2.26
Parameters
interval
an interval within the timezone