How long does it generally take writers to write a 3,000-word blog post of something they don't know about?

It can take hours if you take research done in parallel to the writing process. That time can be reduced if you simply start with your perception about the topic; this way it would kick your mind into gear and start thinking about it; also facilitating research.

Based on my experience, it takes at least two hours for me to write a 3,000-word blog/article. This is excluding the research I do on the topic.

  I think they should read more and more before writing

Searching & Reading increases your words fastly

Thank you for your lovely invitation