In the following document, the expression 'production minutes' comes up multiple times:
The full source of the document can be found here
What does this expression mean, in terms of anime production?
Based on the quotients of the production minutes over number of works and given the context that these numbers are referring to increasing numbers of theatrical anime releases, I believe the term "production minutes" is referring to the length of each anime.
For example, in 2000, 31 theatrical anime were released, each being an average of 61.29 minutes, while in 2014, 74 theatrical anime were released, each being an average of 65.05 minutes.