The "maximum" is limited only by the resources available on
your PC to create the file, and those on your user's PC to view the
published output. From a practical viewpoint, you should consider
that the longer the project is, the more difficult it becomes to
navigate through and find/fix issues during editing;
for example, if an object like a highlight box becomes
corrupted, it is easier to isolate it and correct it in a 30 slide
project than in a 150 slide project.
The maximum, or optimum, number of slides may also vary based
on how large hte project is in physical dimensions. A recorded
movie at 1000pixels by 750pixels is going to max out your resources
more quickly than one of a smaller size. Also, a movie that
contains a lot of full-motion slides will nearly always be larger
(bytes) than one made up entirely of screen backgrounds. And
because slides can be set at a variety of "video quality" settings,
a movie in which all slides' video quality is set to "High" will
always be larger than the same physical sized movie with video
quality set to "Standard" on all slides. Those are just a few
considerations. I didn't mention the inclusion of audio, or many
other items that can make a project larger or smaller, affecting
the ability of your PC to edit it, or the end-users' PC to play it.