It typically takes 7-1\2 hours to film each Boardroom session. Among other things that end up on the "editing room floor" are expletive-laced interactions and heated exchanges that make the ones that are actually aired seem tame by comparison.
Though the show really does take place at Trump Tower, the Boardroom is actually a set built specifically for the show. There are sixteen cameras continuously running while a Boardroom sequence is being shot. Many cameras are positioned behind what appear to be large mirrors that surround the Boardroom. The door that Donald Trump uses to enter the Boardroom actually leads from a narrow room that houses multiple cameras hidden by mirrors. It just looks like a hallway from the camera angle used. Trump's red chair sits upon a raised platform about 4 inches high in order to make Trump appear to tower over everyone else (despite Trump already being 6'3''), emphasizing his supreme authority.
As described in an interview with applicant Tammy Lee, during the first season of The Apprentice (2004), the ending clip each week showing the fired applicant exiting the Trump Tower and entering a cab had actually been filmed during one of the first few days of production before the contest started to cut down on the cost of having to set up for such a shoot each week. Every contestant had this clip filmed regardless of whether they were actually fired or not. From the second season onward, the fired contestants were actually filmed leaving the building after they were fired.
Series creator Mark Burnett originally conceived of the contestants in the first season being divided into college graduates vs. those who finished only high school. However, of those who applied to be on the show there were not enough credible contestants who did not graduate from college. As a result, the teams were instead divided into males and females. The popularity of the show caused a very large number of people to apply to be contestants and the producers were then able to choose a full team with only those with high school educations that was more or less evenly matched with those who graduated from college. This became the premise of the competition in the third season.