I'm not sure if they're totally necessary but each time that I visited I've made an appointment. They have wonderful front desk Personnel so if it's an emergency I'm sure they would take you.
I believe that in general an appointment is needed. I recently got a same day appointment, it depends when you call and how busy they are.
They do take emergencies when open and also leave appointments open if people need an appointment that day. They're very accommodating. Best to schedule though if you can.
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