The phrase "appointed day" refers to a specific day that has been chosen or decided for a particular event, action, or purpose. It represents a predetermined and scheduled day for something important to happen. Full definition
They will come unto thee on foot and on every lean camel; they will come from every deep ravine, (27) That they may witness things that are of benefit to them, and mention the name of Allah on appointed days over the be-ast of cattle that He hath bestowed upon them. (religion.blogs.cnn.com)
The extraordinary master suite adjoins a fully appointed day spa and features 5,600 square feet of living space, fireplaces in its lounge and bathroom, and stunning views. (luxuryretreats.com)
The well appointed day boats depart twice a day for Ras Mohammed, Tiran and the local dive sites - over 30 in total so each day is a new adventure. (scubatravel.com)