How to make Data Access Objects non-blocking?

I'm learning about the Data Access Object pattern, which provides access to a source of data, such as a database. This answer to another question provides the following example:

interface EmployeeDAO {
    List<Employee> findAll();
    List<Employee> findById();
    List<Employee> findByName();
    boolean insertEmployee(Employee employee);
    boolean updateEmployee(Employee employee);
    boolean deleteEmployee(Employee employee);
}

I see similar examples in other answers and articles around the internet. What confuses me is the fact that reading from and writing to a database often take a while, in which case these examples (particularly the find...() ones) would not be very practical as far as I can tell. That is, blocking during a find...() call would probably not be desired behavior.

I'm thinking it could make sense to create a Listener interface (EmployeeDAO.Listener) with methods such as void EmployeeFound(Employee employee), but I'm surprised I haven't seen this before in DAO examples. I wonder if I'm just not understanding Data Access Objects and/or if I'm missing a more obvious approach.