class ActiveSupport::TimeZone

def at(*args)

Time.at(946684800, 123456.789).nsec # => 123456789
Time.zone = 'Hawaii' # => "Hawaii"

A second argument can be supplied to specify sub-second precision.

Time.zone.at(946684800.0) # => Fri, 31 Dec 1999 14:00:00 HST -10:00
Time.utc(2000).to_f # => 946684800.0
Time.zone = 'Hawaii' # => "Hawaii"

of +self+ from number of seconds since the Unix epoch.
Method for creating new ActiveSupport::TimeWithZone instance in time zone 
def at(*args)
  Time.at(*args).utc.in_time_zone(self)
end