That's what I said to the support guy over the phone, why can't I just walk in and walk out 30-40 mins later with a replacement. Doesn't sound like rocket science. His response was, jokingly: "you've never been to an apple store, have you?"
Honestly though, I don't see how swapping an obviously broken product for a new one needs an appointment that's over a week out.
They don't replace them on the spot anyway. All Apple Watches are shipped to the repair center and examined and then they decide what to do.