The time involved in building a website can broken down into three main categories:

1) Theory / Conceptualization / Philosophy of Web Design

40% of the time can be spent on simply conceptualizing & communicating what the site needs to do.

2) Building Core Site / Internet Engineering

40% of the time can be spent on actually building and coding the site.

3) Maintenance

20% of the time would be spent in maintaining the site, including overseeing backup processes, upgrading software, minor bug fixes, ect..