Simple plugin for time played

PlayTimePlugin.java

import org.bukkit.Bukkit;
import org.bukkit.OfflinePlayer;
import org.bukkit.command.Command;
import org.bukkit.command.CommandSender;
import org.bukkit.configuration.file.FileConfiguration;
import org.bukkit.configuration.file.YamlConfiguration;
import org.bukkit.entity.Player;
import org.bukkit.event.EventHandler;
import org.bukkit.event.Listener;
import org.bukkit.event.player.PlayerJoinEvent;
import org.bukkit.event.player.PlayerQuitEvent;
import org.bukkit.plugin.java.JavaPlugin;
import org.bukkit.scheduler.BukkitRunnable;

import java.io.File;
import java.io.IOException;
import java.time.Duration;
import java.util.HashMap;
import java.util.Map;
import java.util.UUID;

public class PlayTimePlugin extends JavaPlugin implements Listener {

    private final File timePlayedFile = new File(getDataFolder(),"timePlayed.yml");
    private final FileConfiguration timePlayedConfig = YamlConfiguration.loadConfiguration(timePlayedFile);

    private final Map<UUID, Long> sessionTimes = new HashMap<>();

    private final BukkitRunnable saveTask = new BukkitRunnable() {
        @Override
        public void run() {
            try {
                synchronized (saveTask) {
                    timePlayedConfig.save(timePlayedFile);
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    };

    @Override
    public void onEnable() {
        getDataFolder().mkdirs();
        getServer().getPluginManager().registerEvents(this, this);
        saveTask.runTaskTimerAsynchronously(this, 6000L, 6000L); // save every 5 min
    }

    public void onDisable() {
        saveTask.cancel();
        saveTask.run(); // Final save on shutdown.
    }

    @Override
    public boolean onCommand(CommandSender sender, Command command, String label, String[] args) {
        if (args.length > 0) {
            sendPlayTime(sender, Bukkit.getOfflinePlayer(args[0]));
        } else {
            if (sender instanceof Player) {
                sendPlayTime(sender, (Player) sender);
            } else {
                sender.sendMessage("You must specify a player to use from console.");
            }
        }
        return true;
    }

    private void sendPlayTime(CommandSender sender, OfflinePlayer player) {
        Duration duration = Duration.ofMillis(getTimePlayed(player));
        // You could make the output prettier here.
        sender.sendMessage(duration.toString());
    }

    public long getTimePlayed(OfflinePlayer player) {
        UUID uuid = player.getUniqueId();
        long time = 0L;

        if (sessionTimes.containsKey(uuid)) {
            time += sessionTimes.get(uuid);
        }
        time += timePlayedConfig.getLong(uuid.toString(), 0L);

        return time;
    }

    @EventHandler
    public void onLogin(PlayerJoinEvent event) {
        sessionTimes.put(event.getPlayer().getUniqueId(), System.currentTimeMillis());
    }

    @EventHandler
    public void onLogout(PlayerQuitEvent event) {
        Player player = event.getPlayer();
        UUID uuid = player.getUniqueId();

        timePlayedConfig.set(uuid.toString(), getTimePlayed(player));
        sessionTimes.remove(uuid);
    }
}