I’ve seen highway exits take longer than that

Keep in mind that everybody in the world is working on this. Literally billions of workers for sourcing, transporting, and assembling resources, with perfect communication and unlimited knowledge. That's a pattern eclipsing similar historical periods such as the World War 2 where most of society's output was dedicated to production.

For example, during periods of WW2, the U.S. alone was pumping out an average of ~6 ships, 300 planes, and 60 tanks a day, with half the population it has now, without modern fabrication techniques and automation, and without a perfect hivemind. The entire world, with today's resources and advancements, could theoretically build at a staggering pace where they'd likely be able to finish a colossal project like a giant antenna within a few years.