Well, i can understand sometimes why processing 2 films in one tank, but why not just go with processing each in different tanks and using the proper time? I don't know how much you save time or developer by doing this, if i process only 2 films and say using concentrate developer without dilution then i can reuse it for another film when i am done with one, i am not good in developing so i don't want to imagine going this route, but i may try doing this one day if i have 2 rolls exact the same instead of 2 different films.