The great people of Nairaland I greet you all

There is one possible major grammar abnormality that I've contemplating about of late. It's about the difference between "How was your day," and "How is the day".

According to the dictionary: Day is a period of 24 hours beginning at midnight : one of the seven time periods that make up a week;

or

The part of the day when people are usuallly most active and when most businesses are open.

These two definition defines that the word "Day" is not possessive. Yet how come that almost all the professors (including the ones in English), Students (Including the first class sets), and others beyond the scope of the examples I gave like attributing the word "my" to a day rather than the day. Are we the creator of the day, is it buyable, do we own it because I don't just understand.

Am I overthinking or correct, let's hear your contributions on the topic