Felix Salmon once advised me that it doesn’t matter when you post a blog. People read all the time and check their feeders in the morning anyway.
Having experimented with this a bit I can say that its more or less wrong. Especially with the rise of twitter, it makes an enormous difference both in traffic and linkage when a blog piece posts.
Posting early morning or very late afternoon seems to work best.
In the early morning professional bloggers seem to be searching for their stories and pick up on an interesting tweet title. In the later afternoon they seem to be putting together their link dumps and are likewise sensitive to an interesting headline.
In keeping with long standing research headlines also seem to be a big deal. Not just with readers but with professionals as well. Presumably they are simply looking for something that will appeal to their readers. Lets say that