ActiveSupport、Time.use_zone

everyday Ruby 
>> require "rubygems"
=> true
>> require "active_support"
=> true
>> Time.local(2008)
=> Tue Jan 01 00:00:00 +0900 2008
>> Time.use_zone('Hawaii') { p Time.zone }
#<ActiveSupport::TimeZone:0x406aa8fc @name="Hawaii", @tzinfo=#<TZInfo::DataTimezone: Pacific/Honolulu>, @utc_offset=-36000>
=> nil
>> Time.use_zone('Hawaii') { p Time.local(2008).in_time_zone }
Mon, 31 Dec 2007 05:00:00 HST -10:00
=> nil