How long did it take to build the mausoleum
The link that you provided does not come right out and say it, but it looks as if it took the workers something along the lines of 37 years to build the mausoleum.
The link tells us that Qin Shi Huang Di came to the throne of Qin (he hadn't yet conquered all of China) in 247 BC. It says that he then had his people decide on a good place for a tomb and start building. This does not tell us how long it took for them to decide on a good place, so we do not know exactly how long they worked on the tomb (at least not from this source). We do know that the emperor died in 210.
So if they got to work in the same year he became king of Qin, they worked 37 years on the mausoleum.