Originally posted by Yamaneko
Well, depends on your take on it. If you're talking about from the time in the Reactor, then yeah, it was a day or two. However, Sephiroth spent that day or two in the Shinra Mansion, reading. Hard to tell at exactly what point he went nuts. So, I'd say a day, at most.
Sephiroth 'locked' himself (as so its says) in the Shinra Basment. He was reading for a while. When Zack (Cloud in his story) went to the basement, he checked up of Sephiroth. A few days later the Shinra Troop (more than likely it was Cloud) told Zack that something was wrong with Sephiroth. Zack went downstairs, got a monologue by Sephiroth, was pushed aside, and then Sephiroth left the mansion. If he didn't killed the troop, I dunno. But what I soeculate is that CLoud was the troop, he went outside looking for Sephiroth when he heard screams, and burning villages, and was then attacked by Sephiroth or passed out from the smoke. As you saw, the troop laying in front of Cloud's house WAS Cloud, and Zack was the sane one. Then it goes to the Mako Reactor scene.