I'm actually a mix from scratch c-41 guy, which makes me an outlier. I have nothing against kits, but have heaps of bulk dry chemistry from b&w, so the idea of colur mix up's don't scare me off.

Developers are the most fragile; most don't last well once mixed, and last even less time once partially used. I currently have 8 reels of films loaded ready to go in the c-41 chems that I plan on mixing tonight, tempering starting tomorow morning before I go to work, and processing tomorrow night. I am extra strange; I developed a c-41 replenisher to keep uniformity as the solution is re-used on subsequent batches

If other films come along in the next 2 weeks, I can process them also, but I don't count on it being reliable and true on all colour layers as it was when it was fresh.

I use a stop bath after the developer in my process. It is simple; 10mL of glacial acetic acid, or more of 28% or more yet of table vinegar. Then a water bath. Then a bleach that I mix that gives me 22 rolls capacity from 2L of solution, and it lasts indefinitely. Then a water rinse, and on to a separate fixer, that will do at least 15 rolls per litre, and it lasts for a number of months with no problem.

The upshot of this is when ordering kits, or components of kits, don't worry if you get more bleach or fixer than you ned up front; they will last. If you order bulk developer concentrate, store what you don't need right away in small glass bottles, filled to exclude all air, and the product will last longer than the kit maker rates it to.

I hope this information helps, even if it does not directly answer your question.