You are free to continue to use Promo Packs for approved purposes after their intended season is over.
For other promotional materials with a specific use (such as product-specific launch promos), please hold onto them until the next Standard set releases. At that time, you may then use them as you would seasonal Promo Packs.
*As a temporary change to our general promo policy, you may also use leftover promotional materials as sales incentives for sealed Magic: The Gathering products once the next Standard set releases. If a product has been delayed, you may use the promotional material as intended with the product once the product arrives rather than on its original release date.