With raytraced shadows, the bucket size plays a huge effect on the responsiveness. Basically DAZ|Studio needs to finish whatever bucket it's rendering before it will cancel ( I suspect I know what's going on programatically, but I'll save everyone from the geekspeak :P ). So if you're doing quick "spot render" type things, you might consider having a small bucket size. For full renders, the larger bucket should actually be just a bit faster since it doesn't have to come back to get instructions as often and can  just keep processing.

To set bucket size... Go to the Render Settings option and on the Advanced Tab is a slider for bucket size.

For my full renders, I use 128. While I'm spot checking, something around 4-6 lets me abort and twiddle surface settings, or whatever faster.