CREATE TABLE table_51166 ("Episode" FLOAT, "Original airdate" TEXT, "Timeslot  ( approx. ) " TEXT, "Viewers  ( millions ) " FLOAT, "Nightly rank" TEXT)

Original airdate for #6 with 1.246 viewers?
SELECT "Original airdate" FROM table_51166 WHERE "Nightly rank" = '#6' AND "Viewers (millions)" = '1.246'
SELECT "Original airdate" FROM "table_51166" WHERE "Nightly rank" = '#6' AND "Viewers (millions)" = '1.246'