Here are the requirements for ranks
Zombie - 30m + build
Spider - 2h + build
ZombiePigman - 6h + build
Skeleton - 12h + Trust + (no build needed)
Ghast - 32h + Trust (no build needed)
Creeper - 55h + Trust (no build needed)
Blaze - 80h + Trust (no build needed)
Enderman - 100h + Trust + knowledge of commands + application (no build needed)
Herobrine - 135h + Trust + application (no build needed)
Well, that is all the things needed for ranks. So now you know
-SuperUser (user092003)
Zombie - 30m + build
Spider - 2h + build
ZombiePigman - 6h + build
Skeleton - 12h + Trust + (no build needed)
Ghast - 32h + Trust (no build needed)
Creeper - 55h + Trust (no build needed)
Blaze - 80h + Trust (no build needed)
Enderman - 100h + Trust + knowledge of commands + application (no build needed)
Herobrine - 135h + Trust + application (no build needed)
Well, that is all the things needed for ranks. So now you know
-SuperUser (user092003)