I would definitely advise against a walk-in. It’s just a pattern I’ve noticed about (smallish) studios in NYC: everyone’s overworked/understaffed and trying desperately to get their work done during business hours. Unexpected guests, or cold calls, or gimmicks ("Hey I sent you guys a pizza!), sort of just distract.
I cannot speak for corporate offices or extra large agencies.
BTW, feel free to PM if you want to grab a beer during your trip.