it took me almost exactly 99 hours (was at 98 hours and 15 minutes when i started going through teh final dungeon), spread over at least a year and a half, possibly more, i don't exactly remember =)
It took me three tries to beat it. The first time i somehow wandered straight through the castle to the final boss without even realizing that it was possible to undo the locked abilites =) I lost painfully needless to say. I managed to hang on until "Snuggles" showed up and started kicking my ass. (*giggles at tiercel* at the time i couldn't remember if he was supposed to be Snuggles or Fluffy =)
The second time i knew you could unlock the stuff, but i didn't bother since i thought it would be complicated. I just headed towards the end and since i had some idea of what to expect, so i optimized my junctions as best i could under the limitations. I was doing pretty good until Snuggles cast his big spell, and then i was dead =)
The third time instead of following the path towards the end i tried the otehr route, and ran right into a boss that i could defeat to unlock something =) I unlocked three or four things, went to the end, and kicked ass.
So now i am done with FF8, though i may try and beat the game without unlocking any abilites, but that would probably require a fair amount of work. I may do that later, but for now, i'm going to start FF9 =)