Time is a man-made concept so, from a spiritual perspective, when we dream of having to keep an appointment we need to make use of time in the most spiritually effective way. There may be an issue to do with our self-discipline. We can perhaps give ourselves a gift or a reward for good work. There is something that has to be accomplished within a certain time limit. Often the person we have the appointment with may be important. Dreaming of going to an appointment indicates we need to have an aim or a goal. The dream is bringing to our notice something our inner self feels we need to deal with. Missing an appointment suggests we are not paying enough attention to detail. You might like to consult the entries for People and Time.