Nominally NEAR is in a 100 kilometer orbit for about eleven and a half days. This is a timeline of NEAR's time in the 100 kilometer orbit. The numbers above the bars represent the day and hour of NEAR's orbit. For example, 101/18 would be the hundred and and first day of the year, hour eighteen. The dark horizontal bars represent downlink time (time when we can't take pictures because NEAR is pointed away from the asteroid in order to downlink to Earth). The dotted horizontal bars represent times that the NEAR Laser Rangefinder, another instrument on board, needs to take pictures, and the MSI can't. Finally, the blue horizontal lines are times that NEAR can take picures. The numbers across the bottom represent the latitude NEAR covers for each part of its orbit. You can see that usually we pass by each latitude more than once.
However, the vertical purple bar shows the latitudes that we can never image, given these constraints (and assuming the camera is only pointed at nadir).
We also can only send back a certain amount of data per downlink, so that means we can only take a certain number of pictures.
Now, it's also possible that the mass of the asteroid could be greater than we originally anticipated, or less. If it is greater, the 100 kilometer orbit will be longer: fifteen days instead of eleven and a half. If the mass is less, the 100 kilometer orbital times will also be different.