I had a lot of time over the last two years to run a necro on the spare monitor while working absurd hours. I failed quite a few times before finally succeeding. Part of the experiments I did on the mummy quest were hour based. Do not attempt the becoming with less than 240 hours. I picked 240 because that's when Twist did it as Tavlin and I figured he wouldn't have gone earlier than was advisable.

240 hours, 100% spell mastery (you only need certain spells, I wasn't sure which so I did them all), leader of a cabal = 70% chance of becoming. I failed.

My last, that was actually successful, was 175 hours and I had something like a 25% chance.

Judging by Daevryn's comments on officials hours have no affect on the lich quest itself but likely on an imm feeling you're worth the time to quest.