I've always wondered why presidents seem fixated on their "first 100 days." I don't have an answer why 100 is a magic number, other than the fact that it's a nice, round, somewhat big number.
Why not 30 days? Or 90? That would make sense; it's a quarter - a measure used in business.
When I start working with a new client, I often get asked, "How long until we see results?" My advice never wavers. When it comes to a public relations campaign, you'll know if it's working within the first 60 - 90 days. If, in that time, there's no movement in terms of media interest, you're either (1) doing something wrong or (2) there's just no story.
At all costs, I avoid guaranteeing anything in terms of media coverage. My feeling is that any PR pro who guarantees hits is up to no good. You can have an incredible story, seemingly perfectly timed, with every piece in place, but then something bigger breaks and you're toast.
Just ask President Obama. His 100th day is tomorrow and, in all likelihood it will be overshadowed by swine flu.