I read somewhere you can do it easier by not defeating Hades or Lich until the clock has passed 100:00 hours. It then returns to zero, leaving you do it again.

Could be a pile of Zaghnol crap though, I tried it got to 100 hours, and the clock went red, but only then I realised that I had beaten all the bosses up to Kuja. It was the last game that worked on my PlayStation, if you catch my drift.