I've built very simple WordPress sites and had them live online in as little as one day! I've also had sites take months. Most of my basic, small business sites are online within a week or so.
In general though, how soon your website work can be done done depends on a number of things, such as:
The size of your website
The complexity of your design
Any advanced features you need
When your content is ready
Our current client design schedule
Your timely feedback and input on our work