I've stumbled on this yesterday, as I used this for the first time. In my game, which was very SGL-intensive for me (about 6 or 7 so far) I had no wonder to build that time, so I thought why not try the Scientific age thing. I've never used it before, but this would mean now that I could keep up my 4 turn research as 25% increase of science is a lot. But I got about the turn counts you described GA. Luckily Civassist II does it's calculations correctly. But it cost me 5 turns already, but I got a nice amount of gold now.
But what I want to know. C3C says the scientific age lasts for 20 turns. Does this at least work???? This would greatly speed up MM.