Originally Posted by Maka
NOTE: You do NOT need to save Katey. If you leave the safe house at 7:00PM (right after the cutscene, and assuming you have all the bike parts) you will need to save Bob and Darcie (before 8:00PM) and you will get the achievement (before giving Katey Zombrex or fighting Jed). They have to be the last 2 survivors you bring back (+ 2 from department store, + 3 from bowling, + 2 from parking lot - in that order)
Any questions on what I wrote, shoot me a PM.
Changed the info but kept her there since she should still be saved in the playthrough if you want all achievements. Explained she wasn't counted.