I am not one for S ranks to be honest, but sometimes I do like a game enough to play through it again on the harder difficlty. I am playing through Lords of Shadow now and frankly am enjoying it a lot.   
 
I am not that far through the game but I can already see another playthrough on paladin. I've been using a guide to get all the gems I can find so I already am planning to have those out of the way. 
 
The only time consuming thing I can think of is the trials, since I assume some are diffucult you would need to complete them at a lower difficulty, but you still need to beat the level on paladin. So I can see someone having to play levels 3 times at least to get the trial on levels that it is too hard to do in paladin. Googling  found a guide that said 40-50 and another that said 50-60 and one that said 30-60. Should I assume it will take about 60 hours to complete fully or what? If it is that long I may put the game aside for a while.

It took me 33 hours.
 
That was what my save file said for time played, not sure if this covers time where I had to repeat parts of levels but I'm pretty sure it does.

I'm going to wait till the 360 patch is out before trying to S rank this game.

For me an S rank took about 2 weeks after I started playing it. Course I used a handy guide for most of the difficult Trials and hard to find gems. Other than that I had no trouble clearing Paladin difficulty