It also says the mask is required for the duration of travel. If you follow this to the letter of the order, that would seem to even include while you were with your own travel group in your stateroom.
Including while sleeping.
See page 4 of the order [bold added].
In addition, the requirement to wear a mask shall not apply under the following circumstances:
•While eating, drinking, or taking medication, for brief periods;
•While communicating with a person who is hearing impaired when the ability to see the mouth is essential for communication;
•If, on an aircraft, wearing of oxygen masks is needed because of loss of cabin pressure or other event affecting aircraft ventilation;
•If unconscious (for reasons other than sleeping), incapacitated, unable to be awakened, or otherwise unable to remove the mask without assistance;7 or
•When necessary to temporarily remove the mask to verify one’s identity such as during Transportation Security Administration screening or when asked to do so by the ticket or gate agent or any law enforcement official
Presumably by the time it gets to cruising being allowed there would be CDC regulations that specifically apply to overnight cruising that would take into account things like guests in their staterooms, crew in private rooms, sleeping, etc. Or not, but at least spell out that those places are not exemptions if that is the case.
In one of cruise line officials' interviews they said one of the challenges they had with preparing for returning to sailing is that the CDC info so far was not specific enough and they had asked for more specific information but not heard back from CDC. The above kind of specificity is the kind that is needed, for a multitude of safeguarding aspects of returning to sailing, and it seems that is part of what has been lacking so far.