There's downtime in most of the current endgame fights where you can charge a full stack of chakra.

For example,

BisEX: The dragonkiller pulling in delay
RavEX: ...Lots
A1: When Oppressor flies up
A3: Switching forms, Tornado form
A4: The delay after hitting Manipulator a few times after breaking a leg when it charges the raid-wide aoe