Often asked – no simple answer – invariably it depends!
As with all things it depends on budget – the more resource you throw at the site the quicker you can sort it out and “fill it with content”.
Several things you can do to a site that will speed things up:
Get something up with something in ASAP so you can start building your online presence (Even if you throw it away later) etc. Now get the rest of the site build
However a realistic time frame to increase your traffic from zero to around 100 visitors per day is about a year. This is assuming you have 1 person working on your website who understands about SEO.
A big part of the SEO mix is great content using the right keywords. If we have lots of content we can accelerate the website in the search engine rankings.
Making changes of this magnitude needs to be done carefully. In the majority of instances we can massively mitigate the risk and reduce the loss to something negligible – however, the things we would do:
HOWEVER the mere fact that there is change always engenders some form of loss so we would recommend a burst of activity on the site for the 2 months following launch.