Covey's Law of Diminishing Interest (what? you've never heard of it?) states that there is a direct relation between the timing of an announcement and the interest that the editorial community has for the announcement. The law separates editors into three classes: Long Lead, Short Lead, and Daily. Long lead includes magazines like Forbes, EDN and most national publications that come out once or twice a month. Short lead pubs are like Business Week, Electronic Engineering Times. These classes have different interest levels depending on the timing of the release. Their interest levels range from "High Interest" to "Annoyed." The daily press is especially affected by this law and has a corollary that any news involving Microsoft and Intel automatically double potential interest.
Editorial interest is based on several factors, timeliness being foremost. In all cases, the best coverage you can get is when the publication date coincides with the date of the announcement, as long as the information will be of interest to their readership.
For the most part, long-lead journalists will always talk to you no matter how far out the announcement is. As such, before the announcement date, they will always have an interest in what you have to say. All begin planning editorial calendars in late summer and, if possible, will consider adjusting their calendars for the coming year according to your major announcements.
As a rule, if the announcement is of significant interest, all long-leads will want to hear something is coming at least six months in advance. From that point, their interest begins to climb, significantly. Their deadline is, generally, two to three months before your announcement date. Therefore their interest at its highest two months from your announcement date. For magazines like Electronic Design, the quality of the coverage you receive (read: cover placement) improves with the amount of lead time you give them. Most require exclusivity for cover treatment. If you give the long-leads less than two months, it will be unlikely they will be able to cover your product announcement in a timely fashion and their interest will wane, along with the quality of the coverage you receive.
For short lead publications, the lead-time shrinks to under two months. Business Week needs 6 weeks. EE Times needs two weeks. Newspapers and local TV news need a week.
So what does this mean to you? Many companies will post news on their website and send releases with one or two weeks lead time to everyone, then they will blame the PR machine that they aren't getting coverage. If you want to substantially improve the amount of ink you get, start understanding the needs and timing of the press and respond accordingly. You'll build a valuable partnership and respect amid a community that usually gives you heartburn. And if you don't have time to do that, that's why you hire resources that can think strategically and execute tactically.