I'd recommend downloading the app and completing your Rapid Pass profile.It will save you a ton of time. After completing your profile, schedule your appointment online. They will try to honor the appointment time as much as they are able.
Appointments aren't needed but, to help things go smoothly, it's best to call up and set an appointment.
Walk-ins are allowed but an appointment is advised. Red cross.com.
Thanks! Your answer is awaiting moderation.