Without doing research on montages (I’ve only
used them when I’m directing and writing, or
working with a director as the screenwriter
when we’re writing the shooting script, which
is different than a spec script), I have to say
to limit the use of montages. I haven’t used
them for so long I find it hard to remember
how long they should be.

You want to be careful with montages. For a
new writers, some actors, directors and
producers look at new screenwriters using
montages as amateurish. Some would also
look at it as directing, which could cause
some negative feelings.

Montages are usually used in shooting scripts.
That means that the director working with
the screenwriter makes the decision, “Let’s
put in a montage here.” The director is
thinking in terms of the visuals and the flow,
how they fit into and tell the story. The producer,
on the other hand, would look at a way
to use montages to save money.