If you are new to blogging, and looking to improve, just keep practicing. Some great blogs posts are worthless to other demographics, and sometimes a 10 minute post is what you'd end up as your most popular content.
Speaking from personal experience, I spend about 3 hours minimum on a blog post. I write in markdown, and of I have to create graphs or diagrams, I spend more time. There are some posts that took me a week or so to complete.
It is important to know why are you making the post. If it is only a hobby, that is good enough. If it is the technical blog to sell a product, it may need more polishing.
Some people recommend to show the advanced draft/almost final form to a few friends or coworkers to get feedback.
If you're writing a comprehensive tutorial for a new framework or design pattern and including tons of code samples and resource links, that could easily take a good few hours, days or even weeks. Same goes if the topic is kinda niche and you're writing for experts in the field, like how to program an in browser VR experience using the canvas element + multiple libraries and frameworks and cutting edge ES6 features.
On the other hand if your post is a bit more modest and mostly deals with a fairly familiar, limited concept, it could probably be done in an hour or less depending on your personal expertise.
As others have stated here, it could be as little an hour to as long as a few days.
There is, however, a framework that I use to speed things up a bit and put probability a bit more in my favor when it comes to helping my potential reader to understand better what I'm trying to explain.
I share some tips on the ways in which you may do this here: https://fromtoschool.com/why-most-programming-tutorials-are-....