module DateAndTime::Zones

Date.new(2000).in_time_zone('Alaska') # => Sat, 01 Jan 2000 00:00:00 AKST -09:00
Time.utc(2000).in_time_zone('Alaska') # => Fri, 31 Dec 1999 15:00:00 AKST -09:00

and the conversion will be based on that zone instead of Time.zone.
You can also pass in a TimeZone instance or string that identifies a TimeZone as an argument,

instead of the operating system's time zone.
This method is similar to Time#localtime, except that it uses Time.zone as the local zone

Date.new(2000).in_time_zone # => Sat, 01 Jan 2000 00:00:00 HST -10:00
Time.utc(2000).in_time_zone # => Fri, 31 Dec 1999 14:00:00 HST -10:00
Time.zone = 'Hawaii' # => 'Hawaii'

if Time.zone_default is set. Otherwise, it returns the current time.
Returns the simultaneous time in Time.zone if a zone is given or

def in_time_zone(zone = ::Time.zone)
  time_zone = ::Time.find_zone! zone
  time = acts_like?(:time) ? self : nil
  if time_zone
    time_with_zone(time, time_zone)
  else
    time || to_time
  end
end

def time_with_zone(time, zone)
  if time
    ActiveSupport::TimeWithZone.new(time.utc? ? time : time.getutc, zone)
  else
    ActiveSupport::TimeWithZone.new(nil, zone, to_time(:utc))
  end
end