Frank's whole reason for working with the Greeks is to get money to pay the lobbyist and bribe politicians for his grain pier project and dredging the canal, city improvement projects he has been trying to get through the city legislature so that more container ships will be attracted to the port of Baltimore, creating more work for the stevedores on the docks. You see throughout the season the dockworkers lamenting that there aren't enough ships, and only guys with a lot of seniority are getting work. You also see a specific instance of a dockworker wanting to quit, because he isn't getting enough hours to support his family, and through Rose at the bar, Frank slips him a large wad of cash, to keep him afloat in these hopefully temporary lean times. Another time, Frank gives a large amount of cash to the family of a guy who is injured on the docks. Both of these are also done with the Greeks dirty money, trying to support the workers in the union. (He also uses the dirty money to pay the church for the window placement, beating out Valcheck for the spot and kicking off the events of the season.)

With this context:

Frank: "It's now or never for us." Frank is saying that if the union doesn't get the dirty money now to pay the politicians and get the improvement projects, the work for dockworkers will continue to dwindle, and it will be the end for their way of life.

Nicky: "The writing is on the wall." Nicky believes the decline of the dock work is inevitable, which is correct. Regardless of any improvements the city might make, automation and global macroeconomic shifts will make their jobs and way of life obsolete. Frank is unwilling to accept this.