With the amateur kits you re-use baths (within a limited time). After a certain number of runs the processing time is prolonged.
If the maximum film-capacity of the solution is employed in one run, an intermediate time is chosen.

see for example the Tetenal sheet:
http://www.tetenal.de/opener1.htm?fi...ges/390137.pdf

So far I did not yet come across a perfect manual text...