The Rush feature helps you break through a certain number of stages during adventuring in the DragonSky world.
Initially, using Rush helps you skip 10 Stages. However, you can further increase the number of stages to be skipped by upgrading its own section in the Lab.
The Rush recharges every 90 minutes. You can also reduce the recharge time from the Lab upgrades.
In the beginning, you can hold up to 2 Rush charges at once. But you also can upgrade the limit via Lab upgrades.
Rush cannot be used to skip your Best Stage.