developing film help

hi! ive been developing film with the cinestill cs-41 kit for about 4 rolls of film now. i was wondering how to compensate for the developer starting to lose potency. there are instructions on the manual but they're honestly making it sound really confusing. how should i increase the developing time and after how many rolls do i know to do that? i know the blix can be used for longer, but when will i know it needs to be remade? thanks so much:)