I also soloed this as NIN/WAR, that's probably the best sub becuase I didn't get hit and had to kill Evil Oscar before I ran out of time. Kittyn explained a good strategy, however of all the times I failed there were certain things I forgot that were important.
Equip: Haste set and melee set (also had debuff set becuase he resists stuff often) that doesn't slow down youre movement, use NIN AF boots nighttime.
When you hit and run, DO NOT try to run past it if it warned you several times unless youre stuck in a corner. Even with NIN AF I would get stuck in its AoE. Better to hit then run back. Also, don't run too much, when I played it too safe I would easily run out of time. Time utsusemi Ni so that you can DD without getting hit. You have to keep using blind/berserk/warcry and hit him before 30 minutes passed. You can use food and a daedulus wing to save time.