They work 24/7. 12 hour shifts "day" and "night" with 3 and 4 days off each other week. They also distribute the work properly in parallel and have the perfect visionary (Elon) and capable leadership / lead engineers, fixing on mistakes and iterating. Probably it's forbidden to work like that in a lot of other developed countries, which basically only allow for 8 hours of work Monday to Friday. And also lack the proper leadership.