Meeting duration as a function of the number of participants

My conjecture is that a meeting involving $N$ participants takes a time $T$ given by:

$$T(N) \, \text{[in hours]} \, = \exp (N/\; 7) -1$$ This only applies to unstructured meetings (with no official hierarchy) and is fairly insensitive to the topic at hand. The time ranges from 20 minutes for $N=2$ to 4½ hours for $N=12$.

For any meeting larger than about ten attendees one should either designate a chairman or schedule a lunch break.