Minecraft wiki entry for Hopper, associated text: Hoppers also have a "transfer cooldown" time. After pulling and/or pushing items, a hopper waits 4 redstone ticks (0.4 seconds, barring lag) before pulling or pushing again (a transfer rate of 2.5 items per second, barring lag). A hopper that has an item pushed into it from another hopper also starts a 4 tick cooldown period, regardless of whether it pushed or pulled items itself. Item entities can be collected at any time without affecting the transfer cooldown time. The transfer cooldown and the Bedrock Edition collection cooldown are independent of each other.