Stage 5 of the John Van Caneghem Tournament

Hypothetically speaking, if the GHOST had different starting conditions – specifically, if it increased the city's level by +1, then on the 10th day, it would be possible to reach city level 15 (which is necessary for building the Grail). And then it would be REALISTIC to build the structure on the 11th day! At least, I had the opportunity for my hero to be in the city on the 11th day with the Grail!
But as it was, I had to spend more time clearing the territory and collecting mercury, and as a result, I built the structure on the 12th day.
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To be more precise, the Grail can be delivered to the city on the 10th day, or even earlier. I did exactly that in my Walkthrough, but I didn't know about the requirement of city level 15 (the buildings themselves are cheap and don't cause any problems), because I only mined the Grail once – in the 5th mission of the 1st Campaign of the original game. Realizing that all my calculations were wrong, I quickly reworked the Walkthrough to 12 days, but I didn't try to optimize the parameters, because I was overcome by great laziness. And if someone tried harder, they probably won.