Your comparisons between render times are very far away from really being comparisons. To determine the difference you need the same render scene, the same settings and only then, this would be relevant. Sickleyield posted a scene on the official Daz forum, to compare systems and render times.
There are so many things, that you can do to either speed up you render time, or slow it down in order to get a better result. For example if you're using 95% convergience or 99,9%, depending on how much iterations have to be rendered, this could make a huge difference. Another very important part is, if you are using Optix or not, this will Speed up the render time significantly, if your hardware is fast enough.
Then the render is important, are you using Iray, 3Delight, Reality/Luxus (with Luxrender) or just OpenGL.
DS clearly uses Iray, which is the best choice, but even then there are some very drastic differences between renders. Even lighting can influence render times, so that a render takes less time, or if it is complex, much more time to finish.
That, at least this is my opinion, is the devs problem, the image quality of some of the new images is not very in, because his lighting is crap. But he promised to release a new version of the game every month, so he needs to render all Images in time. If you take all that in account, it means, that the images he used or version 0.6 are finished faster, than the previous ones.
btw: Sorry for off topic.
