CREATE TABLE table_56697 ("PRR Class" TEXT, "Builderpars_m_singles Model" TEXT, "Build date" TEXT, "Total produced" FLOAT, "Wheel arrangement" TEXT, "Service" TEXT, "Power output" TEXT)

When was the build date for c-c wheel arrangement and freight service?
SELECT "Build date" FROM table_56697 WHERE "Service" = 'freight' AND "Wheel arrangement" = 'c-c'
SELECT "Build date" FROM "table_56697" WHERE "Service" = 'freight' AND "Wheel arrangement" = 'c-c'