since

# File activesupport/lib/active_support/time_with_zone.rb, line 237
    def since(other)
      # If we're adding a Duration of variable length (i.e., years, months, days), move forward from #time,
      # otherwise move forward from #utc, for accuracy when moving across DST boundaries
      if duration_of_variable_length?(other)
        method_missing(:since, other)
      else
        utc.since(other).in_time_zone(time_zone)
      end
    end