Some tips for photographing the main concourse that I have learned during my trips to New York City
1. One of the favourite places to setup is on the balcony occupied by the Apple Store. But the balcony is only accessible when the Apple Store is open - 7 am to 9 pm Monday to Friday, 10 am to 7 pm on Saturday and 11 am to 6 pm on Sunday.
2. Tripods are not allowed. If want to do a long exposure photograph, then I use a monopod and clamp it to the edge of the railing with my hand for stability. As well, small tripods on the base of the camera, designed to sit on the railing, are not allowed. The Apple Store is worried about liability in case a camera fell.
3. if the goal is to get long exposures of people in the main concourse, I would recommend early in the morning during the week. There is constant movement of commuters through the concourse. Later in the day, there are tour groups which tend to stand in one place for a few minutes. And, on weekends, there are less people and the Apple Store opens later in the day.