One of the rewards from Milestones is Crate timer reduction. The Crate timer reduction will reduce the time it takes for Crates in your Crate slots to unlock.  
 
If your Crate timer reduction reward from the Season Score is still active, the Express Access Power-up will still be applied. The duration time of the Express Access Power-up will be added to the time remaining for your Crate timer reduction from Season Score.