Why was Christmas chosen as the attack day? (The war of George Washington)

The attack was unsuccessful, but it was just a way to catch everybody off guard (like a surprise attack).

The Battle of Trenton happened December 26, 1776 washington and troops crossed the deleware river with 18 cannons. after crossing they marched 19 miles south for a suprise attack on the british troops in trenton, the colonists won the battle.