I don't think there's a correct answer to that question. I've read that you need to blog at least twice a week. But I know people who blog daily or as the mood hits.
The point of blogging twice a week is to keep your audience, assuming you have one, interested and to keep your name in their short-term memory. Once your name is in short-term memory long enough it goes into long-term memory, which is where you want it so people will remember your name and recognize later.
Of course, this assumes you are writing a novel and want to sell it later. Frankly, I started blogging for my first novel way too late. You should be blogging when you start your first draft because, as long as it takes to write a book, it takes even longer to bring an audience. So you want to start that process as early as possible.
But it is important to remember there are no rules with blogs. So when you start and how often you post to it is really up to you. On the other hand, once you set a rule, stick with it. For example, I decided to blog twice a week, on Mondays and Fridays. And for the most part I've held to that. This lets the people reading my blog know when to expect it and when to check it.
The downside of this is that I get little activity mid-week but I live with that because I'd fall over dead if I had to blog more than twice a week.
See you Monday.