Don't try to put plot points on specific page numbers, says the screenwriting guru.

Question: What's the worst screenplay-writing advice
you've ever heard? Robert McKee: That there are
certain points, certain pages in fact, in which certain things must
happen.  You got 120 pages—although screenplays are getting shorter,
because the emphasis on spectacle becomes greater and greater... And so,
anyways, say 100 pages.  And properly typed in the right format, a page
is equal to a minute of time.  And so they say, at a certain page,
therefore at a certain minute, more or less in the film, there must be a
major turning point of some kind, or expositional point, a revelation
of some kind perhaps.  And that the worst advice is to—many, many books
that say certain events must happen at certain pages in a screenplay.  I
mean, that is the most destructive possible thing to say to a young
writer.  And to actually destroy a young talent by actually convincing
him that he has to pretzel his work into these page counts, that is just
terrible.  But there is a rhythm, and in order to reach
anything like a satisfying limit of experience for these characters,
generally, you need a minimum of three major reversals.  Okay?  And you
spread those... it could be four or five, I mean "Raiders of the Lost
Ark" was in seven acts.  It could be seven, eight, nine acts structures,
I mean in "Speed," if you counted the major reversals in a chase film
like "Speed" or whatever, it's probably nine.  Every ten minutes
something explosive happens.  Right?  But three is a minimum.  And if
the film is, again, 100 minutes long, and you're going to space those
three out in some kind of fashion, then clearly one of these is going to
happen, perhaps at the very beginning.  There may be another one
somewhere in the middle and maybe one toward the end, or it could be the
first one happens like 30 minutes in, and the next one happens like 90
minutes in, or whatever.  Okay, so you can have, obviously if they have
100 minutes of storytelling, you can't have three major events happen,
bang, bang, bang, in the first 15 minutes and then leave 75 minutes
worth of resolution.  Okay?  Nor can you make somebody sit there for 75
minutes in which nothing happens and then bang, bang, bang three things
happen in the last 15 minutes.  So, obviously these events have to be
distributed with a certain rhythm.  Exactly what that rhythm is, is so
idiosyncratic to the nature of the story that is being told that you
cannot predict, or demand that they happen on certain pages, but you can
point out to the writer, of course that there is a rhythm and that you
have to hook the audience's interest, hold it, and progress it for up to
120 minutes, two hours, even more in many films.  And to do that you'll
need at least three major reversals and then you've got to work out how
to distribute them.  So, there's certain forms.  There's a
form, but by the page is a formula, and that formula kind of thinking is
very destructive.