The general recommendation in the literature I have read (both online and in older printed material, e.g. BJP Annuals) is that the Sulfuric and Permanganate solutions are made up separately and only combined just before use, as the mixed bleach has
The useful life of this bleach is short but it should last for an hour or so. Long enough for use a session of making paper negatives. if it appears to be no longer working or only partially working then it should be discarded. Permanganate bleaches soften the emulsion so treat your paper negatives with care. It is important that the bleach not become alkaline as this may cause staining.
A rock pile ceases to be a rock pile the moment a single man contemplates it, bearing within him the image of a cathedral.