That is not what Acken wrote. He is saying that it could take 120 turns for a GS to be worth planting rather than saving to bulb. So plant before T150.
I did some calculations on a T130 Academy in the NC city. Assumed a T110 Education, T160 ST, T200 Plastics, T220 Atomic Theory, and a T270 SV finish. Also assumed Rationalism opener in T140s (this is does not affect the calculation by that much). And T180 Free Thought.
I am not sure if T220 Atomic Theory and T180 Free Thought are realistic, so calculation may be slightly off.
Also assumed 1 Bulb for ST and one bulb for Plastics.
Up until Plastics (T200) that academy has generated a total of ~1600-1700 Beakers (I included both bulbs, but did not factor any possible RAs).
Assuming 1-2 bulbs between Plastics and Atomic Theory, and a total of 12 GS over the course of the game, at T270 that academy will have generated a total of ~5500-5700 Beakers. This factors in the remaining 9 bulbs (which will generate ~2200-2300 beakers from that academy), but not any RA. I also did not consider the ISS bonus, nor the New Deal bonus.
I think an acceptable late game bulb would be ~8000 beakers, so saving the Scientist would give in the end more beakers.
There is also the discussion of how the science milestones are affected by the academy, but even in renaissance the academy gives 16.456 beakers, while ST costs ~1600 beakers. I don't think the absence of the academy delays ST and Plastics by more than 1-2 turns. But even by delaying plastics for 2 turns you still get the last tech earlier because of the extra scientist.
I don't really know how RAs will be affected by the academy, a bulb before Plastics, only gives on average 140-150 extra beakers because of the academy, so I expect a RA to give similar extra beakers early game. I think that with multiple RAs (eventually boosted by PT) an academy may provide extra beakers and give a faster win, but just by a couple of turns.
I think that even at t160 an academy may be worth it, since in the 30 lost turns, less than 500 beakers are lost, so at T270 the academy would amount to a total ~5000-5200 beakers.
A faster finish time (T250) would probably benefit more from an extra GS late game, so I think skipping the academy may be better, but if the assumed milestones are incorrect calculations may differ.