It depends on many things: your inspiration, how fast the client responds, if your first design draft is good etc.

So, if I am working for one of my sites in 1-2 hours I have it done. I don't need to put too much on the design, so I just create the 'wrapper', since I can code the content afterward. For a client I need to provide a real mockup and this takes time.

We're talking few hours to even a week, if the client is 'fidgety' and can't really know what he's looking for.