Iceland - board 2 hours before sailing in each port?

We’ve done many cruises but the NCL itinerary for our Iceland/Greenland cruise in August says: “Due to security reasons, all guests must be on board 2 hours before sailing. Disembarkation usually begins 2 hours after docking. Itineraries are subject to change at any time without notice.”

Is this just legalese to cover their asses or does this really mean that if we sail at 4pm we have to be onboard by 2pm?? It would really limit what we can do in port…never seen it on any other cruises we’ve done.