I've got to the sky palace, 13 alicorns, 10 ziggurats, 0.09 production. Unicorn Utopia is ages away, merely having 250k unicorns to sacrifice at this time. If I can math right, I need 25 million at this point. Not sure if faster to leave as it is or increase production by spending unicorns. I may or may not eventually spend more blueprints on ziggurauts down the line.
25 million / 2500 = 10,000 conversions
With 10 ziggurats, 10,000 conversions would give 100,000 tears
It costs 10,000 tears to produce 1 black liquid sorrow. You only need 5 to build a black pyramid, and you probably already have 1 from the recent patch. Looks to me like you only need 40,000 tears, not 100,000. So with 10 ziggurats that's 4000 conversions, times 2500 = 10 million unicorns, not 250 million.
So, one twentyfifth as many.
But, you need 10 million, you have 250,000...9,750,000 a .09 unicorns per second, that's 1253 days.
Not sure if faster to leave as it is or increase production by spending unicorns
250,000 unicorns / 2500 per conversion * 10 ziggurats = 1000 tears
Would need to know the breakdown of your unicorn generation rate bonuses to give a precise answer, but just to give a ballpark, assuming you have 1 each, tomb, tower, citadel and palace, and no bonuses from any other source, that would mean your .09/sec is receiving a 90% bonus, meaning your base generation is about .0473/second. If you took those tears and built even a single additional sky palace, that would change your 90% bonus to 140%, resulting in ~.1135 unicorns/second.
10 million unicorns / .1135 = 1019 days instead of 1253 days. Looks to me like spending tears is better if you're in for the long haul. But we're talking about
multiple years.
But, let's say you bought the sky palace to cut it down to 1019 days, then doubled your number of ziggurats to 20. That would cut 1019 days down to ~510. And if you then spend a week or two generating faith to get about 5 million, that would give you roughly a 100% unicorn production bonus, cutting it down to 255 days, which is ~27,540 game years.
If you're going for the 40,000 years achievement, and you're only on year ~3000, you should be able to do it with plenty of time to spare.