I would say that if you already have connections at those companies, it's never too early to start improving those relationships. It's also never too early to start building new relationships -- as long as it's in a non-job-seeking, info-brokering sort of way. If your brother-in-law works at Company X, get him to introduce you to some people, and start building a network there.
When you're in the info stage, you don't want to show up with your resume or even really talk about getting a job. Instead it's about learning about the person, the industry and the company in general.
And I think you want to keep it in the info stage. Be careful about being a pain in the arse, too. They've got a recruiting schedule, and you are suddenly showing up outside of that.
You can be in information broker, play it cool, and work within organic networks and still get the info you're looking for.
IMHO, of course.