A few things about party rewards 

When playing a party, you will receive the rewards ONLY AT THE END of the party. The rewards are not cumulative - they are distinct based on the rank you reached at the end of the party. You can view your final rank when the party is over, upon which you will also see the final leaderboard and your reward.

How to view the leaderboard at the end of a party  

At the end of the party, you will see the screen below. The first screen will allow you to you claim your reward, the second will allow you to view the final leaderboard and take you to the third screen where all winners and rewards will be listed.

How do I know how much time is remaining in a party?

There are a few places to find the party countdown, please see below:

Reward

1st Place winners will be rewarded a badge, this is how to level up your badge.