Time requirement for me depends a lot on the complexity of the project and how many mockups I go through before the client is happy. For a simpler design where the client only requires tweaks and small changes to the first mockup, probably 5-6 hours from blank canvas to styled HTML (although there's usually more styling for content above that).

If the design is complex (for instance, a number of different pages with fairly major design differences) or if the client goes through a number of different mockups before they're happy, then it's more like 8-12 before I've got a completed HTML template.

There's also time fluctuations based on how inspired I am with a project, how much attention to detail I can afford based on client's budget, whether or not I have to think about designing the site's interface as I go, etc.