More specifically in finance/economics. As I understand it, spending at least 5 years in the program is highly beneficial if one intends to work in academia. However, if aiming for industry positions instead some would argue that it might not add as much value as the forgone salary would justify.
This leads me to my question. Let's consider a person who has completed M.Sc prior to entering a PhD program in US in Finance/Econ or another similar field and is on par with the average candidate in, say T20 school. With hard work and long nights, how quickly could such feasibly expect to complete their PhD?
Furthermore, are there major differences between programs in e.g how fast the coursework can be finished, and between requirements one needs to fill before being allowed to graduate? How about supervisors, i.e. are some less willing to let you graduate ahead of time at the risk of suffering some personal reputational damage if it turns out that the candidate falls short of the standards typically expected from a fresh PhD graduate? Any other factors I fail to consider?