These are grammatically correct: Aren't we supposed to have an appointment at this time? Weren't we supposed to have an appointment yesterday? Aren't we supposed to have an appointment right now? These aren't: Aren't we supposed to have an appointment by this time? Won't we supposed to have an appointment tomorrow? You can change the first one to say "Weren't we supposed to have an appointment by now?" If you mean that the appointment should have occurred already. You can change the second to say "Aren't we supposed to have an appointment tomorrow?" Hope that helps.