TransferCooldown tag gets reset when item enters hopper
When using the command,
/blockdata ~ ~-1 ~ {TransferCooldown:1200}
then if an item enter this hopper, it's NBT will change to default. It won't delay 1200 ticks.
When using the command,
/blockdata ~ ~-1 ~ {TransferCooldown:1200}
then if an item enter this hopper, it's NBT will change to default. It won't delay 1200 ticks.