For most PR people, it used to be a 9 to 5 job - unless you worked for a truly large company (the kind that attracted network/cable news coverage), you could safely ignore the world from Friday evening to Monday morning. That's gone now - it hasn't been the case for a few years. This point is made pretty well in an article about the demise of print news:

In the meantime, public relations professionals need to recognize that the days of daily deadlines are also coming to an end. Sooner rather than later, virtually every publication will be deadline-free, because no journalist will ever have to say, "We're going to press at 7:00 P.M." This will change the playing field, giving public relations pros more time to respond to some stories, but less time to deal with breaking news, especially bad news.

Especially for bad news, there's no time lag anymore - you simply have to deal with it in real time. We now live in a world where things can go viral on blogs, on YouTube, on Twitter - the list is endless. At the same time, getting news out that puts you in a positive light is getting harder. The old world of a handful of trade press people you needed to deal with is gone - and the new outlets are doing at least national, and probably global, reporting.