If you want to enter microseconds in a SQL statements, you can enter them right after the time string as a 6-digit number delimited with '.'. '0' will be padded to right if not enough digits. Here are some good examples:

SELECT TIME('1997/01/31 09^26^50.123') FROM DUAL;

09:26:50.123000

SELECT TIME('1997/01/31 09^26^50.000123') FROM DUAL;

09:26:50.000123