Humzah did not pay Zakaat this year on his usual Zakaat due date because he did not have the Zakaat Nisaab.

Answer

If he is sure regarding his Zakaat due date, that is the expiry of 12 months, then he is not liable to pay Zakaat the next day. Zakaat will be due 12 months hence. If he is not sure regarding the expiry of his 12 month period, then it is best that he pays Zakaat the next day when he became the owner of the Nisaab amount.