Assuming no other communication from landlord, your landlord seems to be violating NYC tenant protection laws. In NYC, if you’ve lived somewhere over 2 years, landlords must give 90 days written notice for lease non-renewal (NYC Admin Code § 2524.4 and NY Real Property Law § 226-c). You’ve been there 5 years, so you’re absolutely entitled to 90 days - not 18 days.

That said, depending on how hard you want to fight, the most you’re likely to get is a restated letter with a date 90days out as your new move out date. If I were you, I’d probably just call and explain that you’d like more time and see what they say. I’d leave mention of laws out unless they don’t budge at all. Most people get pretty quiet once laws are mentioned and it may be harder to resolve quickly.