After reconstitution, powdered fixer has a longer shelf life than most concentrated fixers, which shrink much faster after reconstitution - especially in larger dilutions.
Dissolved powder fixers can be stored for up to several months, depending on their use, up to 3-4 months. Small amounts of concentrated fixer left in any container can also deteriorate, causing a white residue to form on the bottom of the fixer container.
When fixing films or taking pictures, remember that it is always better to hold them longer than a little, as fixing too short can lead to an incomplete process and change or damage the image. Also, move the workpiece, photos, or spool to the cork or fuser during machining.