CREATE TABLE table_73152 ("#" FLOAT, "Episode" TEXT, "UK air date" TEXT, "Timeslot" TEXT, "Viewers  ( millions ) " TEXT, "Audience share in timeslot" TEXT)

Name the timeslot for 6.51 viewers
SELECT "Timeslot" FROM table_73152 WHERE "Viewers (millions)" = '6.51'
SELECT "Timeslot" FROM "table_73152" WHERE "Viewers (millions)" = '6.51'