Sailings aren't usually port-to-port- they stop at multiple ports along the way, and at each port, it takes 1-3 days to load new containers and unload new containers, not to mention port congestion, and being re-routed due to weather.

Looking at actual sailing schedules, it takes between 17-21 days.

http://moc.oocl.com/nj_prs_wss/#/sailing_schedules/search?PR...

How are you reaching your 7 day calculation? 7.5k nautical miles at 15-20 knots would be 15-20 days.