Walk-ins take longer, but are accepted. Appointment dates fill up over a week in advance (recently), but make your visit must faster. The registration in their website asks for (does not require) your insurance info (to help defray the cost of the otherwise government sponsored "free" tests). The barcode I received via email was a 2D code (3of9, I believe), but the person curving me in didn't scan it (read the human readable number instead). My last test there, a PCR, took about 3 days, with results via email, a PDF attachment (be sure to put them on you whitelist to avoid missing it in spam). With pre-registration, I've visited twice, and both times this with appointments wait on the left side, for perhaps 5 minutes (while you watch unscheduled visitors waiting the whole time in the right side). Just my experience ...
Yes you can walk in. Although you do need to fill out the application ahead of time and they provide the website or qr code. As soon as you complete the online registration you will be helped out.
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