As people before me have already posted, it all depends on the skill of the person who is doing it. It also depends on what functionality you require and how well you want to achieve it.

For example, you want to create a blog template. The functionality may vary based on your requirement. You can simply have a blog to pen your thoughts. Or you can have a sophisticated publishing platform where users can discuss, post and comment and then certain other functionalities like great SEO which is fully automated and you can also optimize the performance of the blog.

The list of requirements is endless, it is you who have to decide which are essential and which are extra. And, each and every one of these definitely takes time.