Minecraft wiki entry for Redstone_mechanics, associated text: A redstone tick is a unit of time, in redstone, that is equal to two game ticks, 0.1 seconds. Most redstone components take a multiple of a redstone tick to change states. Redstone torches, redstone repeaters, and other redstone components require one or more ticks to change state, so it can take several ticks for a signal to propagate through a complicated circuit.