date_time.rb

class DateTime

  # Adds seconds and returns a new DateTime object
  def add_seconds(secs)
    self + (secs.to_f / 1.day)
  end

  # Subtracts seconds and returns a new DateTime object
  def minus_seconds(secs)
    self - (secs.to_f / 1.day)
  end

end

Required files