"Tomorrow I have a possible date."
Translation:Αύριο έχω μία πιθανή ημερομηνία.
I think the only other way would be to just say "I have another appointment", or possibly " ... appointment scheduled".
It's frustrating that the original comment is now deleted ... I'm guessing it could have been related to the ambiguity of "date" in English ... whether it relates to a social/romantic appointment, or a day on the calendar.