рубин получает Время в данном часовом поясе

Я бы использовал ActiveSupport gem:

require 'active_support/time'
my_offset = 3600 * -8  # US Pacific

# find the zone with that offset
zone_name = ActiveSupport::TimeZone::MAPPING.keys.find do |name|
  ActiveSupport::TimeZone[name].utc_offset == my_offset
end
zone = ActiveSupport::TimeZone[zone_name]

time_locally = Time.now
time_in_zone = zone.at(time_locally)

p time_locally.rfc822   # => "Fri, 28 May 2010 09:51:10 -0400"
p time_in_zone.rfc822   # => "Fri, 28 May 2010 06:51:10 -0700"

Просто добавьте или вычтите соответствующее количество секунд:

>> utc = Time.utc(2009,5,28,10,1)           # given a utc time
=> Thu May 28 10:01:00 UTC 2009
>> bst_offset_in_mins = 60                  # and an offset to another timezone
=> 60
>> bst = t + (bst_offset_in_mins * 60)      # just add the offset in seconds
=> Thu May 28 11:01:00 UTC 2009             # to get the time in the new timezone