In reference to the patent: US20080229509
Is there a date where the product would have to be on the market or otherwise they would lose their entitlement to the patent?
Some countries do require a patent holder to either "work" their patents or be subject to compulsory licensing. India is one example. In the U.S., practicing your patent is not required to keep a patent valid. In fact, you may not even be allowed to make and sell a product that incorporates your patent. An example would be a patent that was an improvement of an already patented product. Without a license on the "base" product, making your thing might infringe an older patent. Or a product that was regulated to the point that you can't make it. You could get a patent on an aircraft design that the FAA doesn't think is airworthy.
First of all, the cited document is a patent application, not yet a patent. It may or may not become a patent and even if it does, the claims may change. To answer your question, however you do not have to market a product to maintain your ability to enforce a patent.