How busy till NYC be on September 11?

All of the 9/11 memorial services aren't anywhere near the cruise terminal, since the WTC site isn't near the cruise terminal. There will be extra security in and around the entire city and metropolitan area at major transportation points, as there is every year on the 9/11 anniversary.

Try to get to Grand Central by 10-10:30am. That gives you 1.5 to 2 hours to get crosstown in a taxi, which should be plenty of time. That way you also won't start worrying about if you'll get there in time.

If you don't have too much luggage and everyone can walk with luggage, you can save money by taking the bus (either M42 to the end at the Circle Line Boat and walk uptown from there, or M104 to 8th ave at 49th street and walk west from there) or the subway (42nd street shuttle to Times Square, then the C to 50th street where the M104 would leave you).

My friend, there will be a lot of security in the days leading up to the date in questioned. Therefore, if you want to get to the Cruise Terminal before 12pm, I would suggest getting there no later than 10:30-11am.

Good luck