Minecraft wiki entry for Piston, associated text: When a piston loses power, its head retracts. Like extending, this retraction starts immediately in Java Edition; or, depending on how it was powered, after 1 tick in Bedrock Edition. It finishes retracting 2 game ticks (1 redstone tick; 0.1 seconds) after it starts. A sticky piston also pulls the block attached to its head, but not any of the other blocks it may have pushed.