So Sir Trollelot explains:
1. There is no set time for the Jigsaw Game prizes to change!
2. The developers monitor how many Mystery Boxes are being opened
3. This helps them decide when it's time for a change
4. A moderator will always announce that they are going to change in the PnF Group, at least one day before they change
5. If you don't have everything you wanted, the prizes will be available for purchase in the Seasonal Shop, and anything that is already in the Seasonal Shop may be used in the Jigsaw Game again in the future!