Showtimes change based on when the park closes...not only in the number of shows, but when they actually transpire as well (would have been easier to just knock off a show time or two if park hours didn't allow for every showing...).
For instance: When the park closes at 6PM, showtimes are 12:30, 2:30, and 4:00.
If it closes at 7PM, the have four shows (possibly the times listed by metro West for 'Monday') and for 8PM, there will probably be 5 shows, and if the park closes at 10, there usually are 8 shows (with cast change after the first 5).
HTH