With Zbrush and level of experience...you'd be surprised what you can do in just 20 mins lol. For me, I'd average your work so far around 2-3 hours, and the Ultimate Weapon closer to 4-5. They aren't polished and still have the zbrush "inflated" look, but these are great base sculpts to get the overall form of each creature, which if anything is more difficult than adding HD detail. Very impressive.
I'm curious, what's your process? Do you start out at low res and sculpt through the whole body and up the poly count as you go along and keep sculpting or do you tackle parts of the body one at a time?