How long should a process take?

"How long is a piece of string?" may be the flippant answer, but it's not a very useful one.

It is possible to predict, with a fair amount of accuracy, how long a process will take if you know how many records must be processed, what is being done to them, what type of machine it is running on, how many i/o buffers are available etc etc

Or, you can run the input file through DFSORT or other high performance utility.

If DFSORT can process a file in 10 minutes (even if it's not doing exactly the same processing...most business applications are I/O bound) and my Cobol program can do it in 15, then I don't spend much time tuning the Cobol because it is probably about as good as it is going to get.

That is just a rule of thumb of course. Your mileage will vary.