From our standpoint as server administrators, configuring a DNN portal (site) is very fast. It takes under a minute to create a new portal within our installation. A traditional web site (configured with IIS) takes about 10-minutes.
From the standpoint of a site administrator (you), this can vary quite a bit. We've had sites launch within 2 days of the administrator having attended training, while other sites take a bit longer.
In general, the amount of time it takes to create your site depends on the amount of content you want available when you launch the site. Consider the most important content first and add lesser content when time permits.