To the best of my knowledge, I don't think that the Zim Kingston was under any pressure to dock, because that was exactly the reason.... Because of the congestion in the port, the vessel was required to wait for many days before they could actually dock, so there was definitely time at hand.
Again, on the pressure on the master, there is a framework book, which we call the international safety management code. The master definitely has an overriding responsibility on the safety of the vessel, cargo and the crew on board.