Order of the day and Order of business

Order of the day noun - The order of business for an assembly on a given day.

Order of business and order of the day are semantically related in program topic. In some cases you can use "Order of business" instead a noun phrase "Order of the day", when it comes to topics like agenda.

Order of business noun - A list of matters to be taken up (as at a meeting).

Order of the day and order of business are semantically related in business to be taken care of topic. You can use "Order of the day" instead a noun phrase "Order of business".