N.J. Admin. Code § 13:71-15.15
All entries or payments except in overnight events not actually received at the hour of closing shall be ineligible, except entries and payments by letter bearing a postmark not later than the following day (omitting Sunday) or entries notified by telegraph. Where a telegram is used, it must actually be received at the office of sending at or before the hour of closing. Such telegrams must, furthermore, state the color, sex and name of the horse, the class to be entered, name and residence of the owner and the party making the entry. Whenever any entry or payment in a stake, futurity or early closing race becomes payable on a Sunday or a legal holiday that falls on Saturday, such payment is to be due on the following Monday and if made by mail the envelope must be postmarked on or before the following Tuesday. If a payment falls on a Monday that is a legal holiday, such payment is due on Tuesday, and if made by mail must be postmarked on or before the following Wednesday.
N.J. Admin. Code § 13:71-15.15