CREATE TABLE table_37989 ("Date" TEXT, "Opponent" TEXT, "Site" TEXT, "Result" TEXT, "Attendance" TEXT)

What date was the Site michigan stadium ann arbor, mi?
SELECT "Date" FROM table_37989 WHERE "Site" = 'michigan stadium • ann arbor, mi'
SELECT "Date" FROM "table_37989" WHERE "Site" = 'michigan stadium • ann arbor, mi'