You may request an appointment for your boss or acknowledge letters requesting an appointment. In each letter, always refer to the reason for the appointment and the suggested time; always request a confirmation.
If a certain time has been requested, and your employer approves, confirm the appointment accordingly. If your boss will be occupied at the requested time, suggest another, and ask for confirmation. Be sure to keep a record of appointments suggested and not yet confirmed. If there is ever an argument that your employer broke an appointment, you will have proof otherwise in writing. For this reason, if the back-and-forth process of setting an appointment moves from the letter to the telephone, always send a letter to confirm it in writing.