I've heard of people doing it in 6 hours, probably if you time it right. Story mode on hard, run through all the bounties twice (so starting before reset) Being good in crucible, getting those bounties too Then strikes to finish off I don't do crucible so it probably took me 20 hours last time, I did find one great shortcut if you already have a character, load up on blue engrams and transfer them to you vault every three levels, your character ends up with much better gear and weapons