The fast ones you see on TikTok were like IBS (Industrialized Building System). The building was prefabricated, the groundwork was done, and the video starts recording as they transport and connect the parts.
Generally it would take about 2 years.
Piling and building the foundation is the bulk of the schedule. This is much harder in dense urban areas where it has to be done carefully.
Then you have all the other pieces - design, manpower, parts, machinery, bureaucracy, tests, redoing failed tests. Then your services like machinery, electronics, plumbing, facades, cleaning up, QA and defect fixing.
High safety projects often go faster because it's accidents that really mess up the schedule. A single death can end up causing months of delays or a hefty "fine".
If you already have a generic design or simple, non clever brutalist design, it goes much, much faster and cheaper.