can you explain that management triangle you mentioned?
It's what Stealth was alluding too as well: https://en.wikipedia.org/wiki/Project_management_triangle
Often summarized as Stealth said. You have 3 components to how a project turns out that are in conflict with each other. You have the scope (how much work you're going to do, and how good the quality will be), the timeline, and the cost. You can't optimize all 3 and if you make changes to one it will affect one of the other two, or both. If you want to make a project cheaper, generally speaking you let it take longer or you reduce scope/quality. Since they're doing the opposite (or at least they're not admitting to changing the scope or quality) then it makes me very suspicious of their statement.
Sometimes large constructions like these have additional costs than just materials and labor. Sometimes permits and concessions expire. There are conditions to development that must be met with work or money. If you don't finish, you pay. There was a case I remember where the watchtower bought land for development. The city approved the development and gave incentives. One was having to make some donation or purchase for the local fire department (if memory serves me well). The real state agency that managed the sale had a clause that said that the org had a number of years to develop the property. If the development was canceled by the org and they wanted to sort of "return" the property, they had to pay a huge sum of money on fines.
So sometimes accelerating the job may cost more in personnel but a lot less in red tape.
I thought about this, but dismissed it because I figured that the original plan would've already been laid out such that inspections, permits, etc were all arranged and timed correctly to avoid any fees and unnecessary costs. Assuming someone didn't botch the planning, would a shorter timeline actually save money normally? While I've had a little exposure to construction, I'm not super familiar and certainly nothing on this scale.
I guess you are saving some money by moving up the completion date by 3 months. They feed all the workers right? Saving 3 months food costs, that's saving something. Other than that, off the top of my head I can't think how it saves them money.
Any savings on food cost would be minuscule unless they've actually reduced the amount of work that will need to be done (i.e. don't build one of the dorms or something). Assuming they're keeping the project scope the same, the only way they save money on food is if there's less waste because they're feeding more people. To get the job done faster, they'll have to bring in more people, so they're feeding people for 4 months less time but they're feeding more people and it balances out.
In most cases, bringing the schedule in (especially in cases like this where there was already a fully developed plan) by throwing more people at it usually results in an increase in total person-hours required to finish the job. The more people you add the more overhead there is in coordinating them, and the more they're stepping on each other's toes and the more you have problems with the right people getting the right information at the right time. That's a big reason that, generally speaking, reducing a project's schedule increases it's cost.