Speak to a local attorney regarding constructive eviction or potential counterclaims against the landlord. Even if three days is permissible, your son may be able to get a small extension from the judge.
Dear Buffalo Tenant:
Do you mean a three day rent demand or an eviction notice from the Sheriff? A rent demand is before the landlord sues the tenant in a nonpayment case. In the lawsuit the tenant presents defenses to the landlord's lawsuit. A defense based on the landlord's failure to repair is allowed by the New York State statutory Warranty of Habitability.
Read about tenant defenses at:
The answer provided to you is in the nature of general information. The general proposition being that you should try to avoid a bad outcome if you can.