It is true that all of the materials must be used at least once. Here's why you need N, hopefully this helps:
[3 Materials Needed] Center 1: (N) (T/W) (P) [ Must have 3 materials b/c you need P here - if it’s in C2 it needs to be in C1; and, P can …
The online tool provides options to change the time allocated. The time adjustment option is the clock icon to the left of the underline/highlight functions.