CREATE TABLE table_name_86 (date VARCHAR, time VARCHAR, meet VARCHAR, nationality VARCHAR)

What is Date, when Meet is 'World Championships', when Nationality is 'United States', and when Time is '1:46.68'?
SELECT date FROM table_name_86 WHERE meet = "world championships" AND nationality = "united states" AND time = "1:46.68"
SELECT "date" FROM "table_name_86" WHERE "1:46.68" = "time" AND "meet" = "world championships" AND "nationality" = "united states"