Yes, had brainfart it's 48hrs. Some other cruise lines have 72hrs?
Anyway, it's a moot point as there are no checks anyway. I'm sure that everyone who had a car sick child on the way to the port, or had a dodgy kebab a couple of days before the cruise also declares it on the health questionnaire?
It's just the cruise companies covering their backs, so they could say they have covid and norovirus protocols in place.