The distinction between labor time and calendar time is an important one! 40 hours of dedicated effort is great, but most people parse that as "1 week" when in reality the available people may only be able to get 10 or 20 hours in a week due to other demands, or it's 38 hours of dedicated time that gets done in 1 week but the 2 hours of security and legal reviews take a month of waiting to finally get completed.