People, who have communication support needs, usually require more time for an appointment because it takes longer for them to communicate. 

You may want to schedule an extra 15-20 minutes or arrange an appointment at the end of the day so that you can go over the allotted time. When appropriate, it may also be helpful to send the person a list of questions that will be asked during the appointment so that they can prepare their answers ahead of time by writing them out, or programming them into a communication device.

If the person needs to follow-up with you after a meeting, discuss whether they will do this via phone, text or email communication.