Is that significant? I'm honestly curious, I'm not sure what being released on a Friday means as opposed to some other day, do people pay less attention to Friday news?
A lot of bad news comes out late Friday, government reports, financials, etc. It's obvious that the Washington Post was sitting on this particular story and decided to post it only after today's Guardian reports. WaPo has done it quite a lot since the leaks came out, either they aren't particularly interested in breaking these stories, or they're abiding by an earlier deal with Snowden since they wouldn't agree to his release timeline.