The Campaign Progression Pass allows you to get gold rewards for your Campaign progress. Once you purchase one of the three passes, you'll be able to claim gold milestone rewards once you've met the requirements listed on each milestone.
If you've already met some requirements before purchasing, you can purchase a pass and get rewarded instantly! You can also buy the pass and complete the requirements afterwards.
There is no expiry date attached to the Campaign Progression Pass. Once you complete the milestones and claim your rewards, the pass is complete. You can only purchase each level of the pass once.