I've done the Evoliths recently, for WC reduction. They are reduced in half from the original potency (each -1 is worth 30 seconds instead of 1 minute), and they do stack with each other. I never found a WC-3, but I have a few -2s and some -1s.
With a -2 stone and three -1 stone, the reduction is 2m30s. Probably not worth carrying around 4 more pieces of gear, but MAYBE you could get it to -2 on head, -3 on body, -1 on hands/legs for a total of -3.5 minutes, with some luck.
This must be done with extreme care, because you're putting on 4 pieces of non-item level gear to do it.
I personally chose not to use the gear because it's not worth it for me, but might be worth it for you. If you have other questions on how it works or how to do it, let me know.
You could put 5 pieces on, but the relic boots (WC) or legs (SV) are probably preferrable for their effects.