The content of your blog encourages people to read your blog. More people reading your blog gives the blog more value. What you publish today will be in your blog tomorrow - and if what you publish today has value, it will have more value tomorrow.
So, what you publish today will make your blog more valuable than what you publish tomorrow. Publish today, revise tomorrow - that's progressive publishing.
If you have an idea for a blog, that truly has merit, you need to start your blog today. Choose a popular yet unique subject, use an available URL, and then publicise your new blog. Don't waste time, and lose blog value, by waiting for the URL of your choice to become available. Keep publishing your blog, and stay ahead of the spam.
Get started today, and do more tomorrow - using a URL that's available today.