You can run, but you can’t hide. Facebook’s biggest user interface overhaul since the Wall, the Facebook Timeline, is now becoming mandatory for all users. According to the company, over the next few weeks, everyone will get the new Timeline. And here’s the important part: when you do, you’ll have just seven days to preview what’s there now, and hide anything you don’t want others to see. [Update: Facebook did not immediately require migration for those whose shrugged off prompts to switch, but plans to push forcibly push Timeline to all users by Fall 2012.]

In case you’re unfamiliar, the Facebook Timeline makes it far easier for you to travel back through your Facebook posts – posts which normally disappeared off your Wall and into oblivion. The posts from these previous months and years are now accessible through new navigational elements on the right-side of your screen that let you quickly travel back in time to the day you were born.

You can fill in data from your pre-Facebook years using the new status update box, which now includes support for adding a specific year and various “life events.” These events include things like marriages, births, deaths, new jobs, trips and vacations, new homes, and other things you might want to record in the scrapbook-like Timeline.

With Timeline’s added ability to find older posts, including those from the days before your boss, grandparents, mom and dad were on Facebook, users will need to do a rapid cleanup on their profiles when the Timeline goes live.

Facebook explains how to hide posts you don’t want to appear on your Timeline (click the pencil to hide, delete or edit a post). You can also use the privacy drop-down to change who can see posts (e.g. “Only Me”).

In addition, the company is releasing a new tool today called Activity Log, which is where you can review all your posts and activity, from today back to when you first started using Facebook. Fortunately, only you can see your activity log.

Previously, users had to go out and get Timeline for themselves. Facebook was specifically trying to not push it too hard. It wouldn’t show News Feed stories announcing your friends had migrated, for example, as the company wanted the Timeline to be an opt-in decision that allowed people enough time to moderate their profile posts. Giving users seven days to do the same is somewhat an extension of that thinking, although could prove troublesome for irregular Facebook users who don’t realize they’ve been migrated, leaving themselves exposed when the week is up.

If you want to be proactive and get the Timeline now, go to the Introducing Timeline page and click “Get Timeline.” Or you can wait until you see an announcement at the top of your profile.

Timeline will also be available on Android, m.facebook.com and iOS.