Ros2 is very time sensitive. So it is usefull to have all computers synchronized to ensure there is going to be proper communication while using ROS2 topics, services and actions.
If you are going to use, or communicate in any way with the ARCOS-Lab humanoid robot, you should make sure that you are synchronized with the robot.
sudo systemctl status systemd-timesyncd.service
If the output says active (running) you are good to go.
/etc/systemd/timesyncd.conf. Make sure to set the NTP server to the IP address of the humanoid robot:NTP=192.168.18.20
sudo systemctl daemon-reload
sudo systemctl restart systemd-timesyncd.service