I have never used Tetenal C-41 but I use Kodak's C-41 and if stored in full, glass, well sealed bottles the working solution will last many months. In fact I have had it last over three years without degradation, hardly changing color. This is in contradiction to Kodak's own literature. I would suggest you try storing the Tetenal this way and monitor it occasionally for color change due to oxidation until you need to use it. Then you will know once and for all if it will keep that way.