What is the best time to patent our product?

Actually, your actual product may not be a valid patent as a whole. Yes, if you could narrow to the core invention of your product, you might find that, just one part of your product might be an invention.

Technically, It is better not to club the patent and the product together. Because, if you find that there is a inventive step, and it is non-obviousness, and if your whole concept sounds positive and there is a space for market potential for developing a product, then it is better to file the patent irrespective of the product development.

Economically and logically, if the product research is at developing stage, and your research is protected by trade secret strategies, then continue product development without a patent. Specially, in the US Market, creating a patent asset is a costly process. Hence, consider patenting at very positive stage of development and market potential.

In March, 2013, the US patent system went to a first-to-file system in alignment with much, if not all, of the rest of the world. Therefore the first one to file a patent application with respect to a particular invention - system, method, machine, product, whatever - is automatically the senior party and will have senior rights offensively if they receive a patent, and defensively even if they do not receive a patent, their application will be published and will serve as prior art against those who file later applications for essentially the same invention. Accordingly, it is in your best interest to file a patent application as soon as possible in order to protect your future rights. If you are still in the development stage, you would be wise to file a provisional patent application for what you have already developed. You must then file a non-provisional patent application or a PCT application within one year from the filing date of your provisional patent application but your provisional patent application will effectively provide you with a priority date relative to others who may file later applications for similar subject matter provided that your provisional application does in fact provide an enabling disclosure of your invention. In other words, the provisional application, just as with a non-provisional or PCT application, must be complete, accurate, and thorough. If you in fact develop your invention further, or develop additional embodiments, you can then file one or more provisional applications within the one year time frame and then file your non-provisional or PCT application within one year from the earliest provisional patent application. A good technique in dealing with subsequent provisional applications is to effectively add the new developments or embodiments to your original provisional application and then use your last omnibus provisional application as your non-provisional or PCT application - in this manner, nothing gets inadvertently omitted from your non-provisional or PCT application.

Your product development process should occur alongside evaluations of how your product might be patentable and, in related fashion, whether your product might infringe another venture's preexisting patent rights. What you certainly don't want to do is "finish" product development, start selling, and then explore patent protection.

There is not a "best" time to patent your product. Indeed, whether you may patent it in the first place is not entirely up to you. Your patent-related timeline integrates your product development and public disclosure timelines, in a sense.

It is advisable to consult a patent attorney in private to evaluate your product and help steer its development with patentability goals in mind.

Steve Weintrieb's answer is exactly what I would have said. I think he covered this question quite expertly. First-to-File has had a great impact on strategy decisions.

Assuming that you have a new and novel invention, and further to Steven Weinrieb's comments, you will want to file an application for your inventive elements before any public disclosure or offer for sale. Not only does this strategy provide you the ability to discuss your invention(s) with investors, outsourcers, future employees, etc. with more peace of mind, but if you do not have a patent application filed (e.g. provisional, non-provisional, PCT, foreign application, etc.) before public disclosure/offer-for-sale, you will preclude your ability to get a patent in certain foreign countries. There are very few countries that offer a 12-month grace period between public disclosure/offer-for-sale and application filing (I believe that the US and Canada are the only two that have the grace period). Filing in other countries may not be on your mind right now, but it could become very important for certain inventions.

With respect to budgetary considerations of "when to file", I usually advise my budget-conscious start-up customers to find initial funding (e.g. family/friends) to file an initial patent application (often a provisional done properly but would be better to have a non-provisional filed - a separate discussion) on the foundational aspects of the product, then put budget into other aspects of the business, talk to investors, etc. and then revisit a solid patent strategy once things get rolling.

Apart from filing strategy, what will you do with a patent if granted? Do you want it to license to competitors? Can a competitors circumvent it? How easy is it to discover someone using your invention? ( so you could license or exclude them?) do you have the money to litigate to enforce it if granted ? Normally allowance is a good 3 years from filing (less if you qualify and pay for accelerated examination) - will your patent have value in that timeframe (e.g., the company will still exist)? Yo can always sell a provisional application or an issued patent, but well before you start the meter on drafting and filing expense you need to answer those basic ROI questions.