When is it time to hire help for your SEO?

When do you think it is time to hire an SEO expert to handle all your internal optimization of your site? You are the only person that can answer that question. Anyone can perform SEO and anyone can maintain SEO, it's just a matter of having the time and the knowledge.
If your business has 5 products/services and is a fairly small operation, chances are an employee may have the time to learn and to perform the SEO that needs to be done. So instead of checking into what companies are out there to perform the SEO, use sites that already exist to learn about the process of SEO like SeoBook for example. This way an existing employee can learn the process of SEO or even hire a new employee to do the work for you at an hourly rate rather than paying someone obscene amounts of money to do it for you. However you do miss the quality of the work, this is a best case scenario for a small business. A larger business may want to take some of the money they have in their marketing budgets to hire a company to optimize and maintain optimization on the site ongoing. The choice is completely up to you, and there is no real answer it's just another judgment call you have to make as a business owner.