Mine states expires 2/24/23, sail by 12/31/23.
So I have less than 4 weeks to book this offer, and it's good for any sailing this year.
When I tried to book a mock cruise on the NCL website, using the 10% FCC offer, I was allowed to use only 1 CruiseFirst certificate. While not using the 10% FCC offer, I was able to use 2 CruiseFirst certificates for the sailing I wanted. So there seems to be some limitations for allowable discount combinations. I will have to call NCL directly to use the MyVegas discount, and see if that can be used together with the others.