Prior to the Internet era, anyone starting a new business would generally launch every component of it at the same time. For instance, if an entrepreneur commenced a new retail store, he would certainly not take out advertisements in the local newspapers before opening the actual store listed in those ads. To do so would not only be a waste of money, but would likely anger prospective shoppers who made the time and effort to visit the store advertised, only to find that it had not yet opened for business, but instead was still under construction or setup. Such a traditional brick-and-mortar enterprise would be best launched with all parts of the business — physical location, marketing, management, etc. — available and revealed to the public simultaneously.
The Web has transformed this business principle, as it has so many others. Advanced features of a commercial website can be rolled out independently, at any time, provided that all of the basic features are present when the site is brought out of beta testing and offered to the general public. The domain name of the site also needs to be in place right from the start. However, this does not imply that it is best to register the domain name at the same time that the construction of the site has been completed, for several reasons.
The ".com" top-level domain is — as intended by its creators — the clear favorite for commercial websites, particularly for companies in the United States. Almost all established firms have registered the domain names that correspond to their trademarks and service marks. Also, an even larger number of new enterprises have secured the most promising domain names for their businesses — namely, those names that are descriptive, memorable, short, and contain the keywords of the respective industry. As a consequence, most of the worthy domain names have already been registered. There is such high demand for the better names that domain name "squatters" will grab numerous names that they hope to be able to sell at a premium in the future. As a business owner who wishes to secure an appropriate name for your new venture, you should register your desired domain name as soon as possible, if only to reduce the odds of losing it to another entrepreneur or a squatter.
Secondly, the longer that your chosen domain name has been registered, the more favorable that search engines will evaluate your website. For instance, Google's search algorithm considers the age of the domain name as one of many important factors, because Google is trying to find and rank sites that are most relevant to the keywords entered in by the user. Sites that have stood the test of time are considered to be more valuable and legitimate, and will, all other things being equal, rank higher in the Search Engine Results Pages (SERPs).
Many honest online business owners are unaware that spammers and other Web scoundrels will register a new domain name, employ a wide range of deceptive marketing and sales practices, and then abandon the domain name in order to avoid the penalties imposed upon it by search engines (and perhaps the authorities); or the bandit will lose his domain name if it is shut down by court order or other drastic measures. Any commercial domain name purchased within the past 12 months can be considered a red flag to search engines. In fact, Google does not even assign a Google PageRank to a site within the first three to four months of the life of its new domain name, but instead keeps it in a virtual "sandbox", which may be thought of as a quarantine for potentially nefarious sites.
You want the search engines to find and index your site — specifically, the domain name and the important keywords within your content — as early as possible, so that when it comes time to formally launch your site, the search engines will give it greater credence, and view your enterprise as a long-term business and not a fly-by-night scam operation. Someone focused only on short-term costs might protest that paying for a domain name while the site is not yet ready to go public, is a waste of money. But nowadays the annual cost of a domain name is extremely affordable, and a fraction of the long-term value to be derived from your domain name enjoying greater perceived longevity. A wise online entrepreneur will oftentimes purchase dozens of variations on her chosen business name, partly to keep her options open in terms of choosing the main name, and partly to prevent her competitors from snatching up those names and later benefiting from her future marketing efforts for whichever domain name she eventually settles upon.
A related factor is the age of the website itself, which is defined as how long the site has had actual content on the Web. Naturally, you will want to roll out a polished site as soon as possible. But if your future site is not yet finished, or has yet to be even designed, what can you use in place of a finished site, that visitors will see when they go to your new domain name? A single Web page will suffice, and it does not need any sort of styling, navigation, or anything else that will be eventually introduced in your completed site. Rather, it is sufficient to have a page that contains at least the primary keywords that you plan on optimizing within your future site's content. You can simply announce your upcoming site — assuming that it is not a revolutionary idea, in which case you do not want to give your competitors a head start.
A third related factor is the length of time for which the domain name has been registered. For instance, if you choose to pay upfront for a registration of five years, then it is clear to search engines that you are in it for the long haul — certainly much more than someone who pays for only one year, which is common practice among spammers and other types of Web miscreants.
So, regardless of how long you think it will take for your chosen Web designers and developers to craft your new site, do not wait to register the domain name(s) that will best serve your online business in the future.