By combining parsing time in given time zone and getting time in different time zone you can easily convert any time represented in string to different time zone:

For example to get time in New York if in Warsaw is 13:27:

warsaw = ActiveSupport::TimeZone["Europe/Warsaw"].
  parse("Sun, 18 May 2012 13:27:25")
=> Sun, 18 May 2012 13:27:25 CEST +02:00

york = warsaw.in_time_zone("America/New_York")
=> Sun, 18 May 2012 07:27:25 EDT -04:00