Wouldn't it be a bit early to start constructing the Death Star this early? 19/20 years before ANH? They managed to build half the second Death Star in the time between ANH's ending and ROTJ. So why would they need 19/20 years to complete the first one? And wasn't the second one even bigger and more powerful then the first one, one would asume that the second one would need more time then the first one.