The turn was completed sometime prior to Better Than Life. HOLLY: I knew you wouldn't get it. Post pod's arrived. RIMMER: What, the mail? HOLLY: It's been tracking us since we left Earth. Now we've turned round, it's caught up. LISTER: Do you mean it's taken three million years? HOLLY: Yeah, that's about average for second class post. Given Lister said in Future Echoes that it would take four thousand years to turn around, we have to assume that Lister and Cat went into stasis for at least four thousand years sometime after Future Echoes and before Better Than Life.