Gst.DateTime.prototype.get_time_zone_offset

function get_time_zone_offset():Number {
    // Gjs wrapper for gst_date_time_get_time_zone_offset()
}

Retrieves the offset from UTC in hours that the timezone specified by datetime represents. Timezones ahead (to the east) of UTC have positive values, timezones before (to the west) of UTC have negative values. If datetime represents UTC time, then the offset is zero.