how to schedule an Asynchronous repeating task bukkit code example
Example: spigot repeating task
Bukkit.getScheduler().scheduleSyncRepeatingTask(plugin, new Runnable() {
@Override
public void run() {
Bukkit.broadcastMessage("This message is shown immediately and then repeated every second");
}
}, 0L, 20L); //0 Tick initial delay, 20 Tick (1 Second) between repeats