Mine Dash is a time-limited event, where you compete with other players. You need to beat levels faster than other players in order to get your rewards.
Mine Dash consists of three stages:
Stage I - 5 levels
Stage II - 10 levels
Stage III - 15 levels
Complete each stage as fast as you can do to move the next stage! If you fail at a stage, you can compete again at the same stage.
Every Mine Dash competition is separated. You can start a new dash right after your current dash is over.