I make up the stock solution - and then store it in several quart bottles. That way, the only bottle that I open is the one bottle that I am currently 'working on' - the remainder stay full and tightly close until I need to use them. That way, the stock solution lasts a very long time. In fact, I don't recall every having any stock solution go bad.
Then, I dilute it to dilution B (or dilution H) just before using it. I have a graduate that I have permanently marked with the volume required to make up 200 and 400 ml quantities of the working solution so that all I have to do is fill the graduate to the line, and then add water. It actually takes far longer to get water to my desired processing temperature than it does to mix the working solution.