CREATE TABLE table_2597 ("Market Rank & City of license /Market" TEXT, "Station" TEXT, "Channel TV / DT" TEXT, "Owned since" FLOAT, "Affiliation" TEXT)

When was the station WLS-TV owned since?
SELECT "Owned since" FROM table_2597 WHERE "Station" = 'WLS-TV'
SELECT "Owned since" FROM "table_2597" WHERE "Station" = 'WLS-TV'