80 percent of engagement around a post happens on day one, and that 60 percent of that happens within the first hour. What was surprising, however, is that this is actually a decrease from the numbers Grigorik has for 2007. According to his data from two years ago, 95 percent of engagement happened on the first day, and 90 percent of that was within the first hour.
From: "Technology Review: Blogs: TR Editors' blog: The Speed of Online Conversation."
This article is a must read - Grigorik believes online conversations' D-day replication is slowing down a bit as our distributed networks increase in size via weak ties, which have slightly slower bonding/sending capabilities.
Social networks are getting more complex via nodal interactions, so our filtering of value slows down about 15%. It'll be interesting to see what happens in another year of social networking distribution.
Will our weak tie/"friend of a friend" human filters cause engagement to drop another 15% or so?