Doesn't work after few (4-5) loops

fetcher.rb

#!/usr/bin/env ruby
require 'rubygems' unless defined?(Gem)
require 'forever'
require 'gmail'

USER_NAME = '********@gmail.com'
PASSWORD = '********'

Forever.run do
  before :all do
    @gmail = Gmail.new(USER_NAME, PASSWORD)
  end
  
  every 10.seconds, :at => "#{Time.now.hour}:#{Time.now.min}:#{Time.now.sec + 5}" do
    unread = @gmail.inbox.count(:unread)
    puts unread.inspect
    unless unread.zero?
      @gmail.inbox.emails(:unread).each do |email|
        email.mark(:read)
        puts email.subject
      end
    end
  end
end

Because :at will not be updated. Why you need it?