We're open seven days a week, 365 days a year.
Payment is due on the first day of every month.
“What day is (it) today?” “Tuesday.”
“What day [=date] is Friday?” “It's the 28th.”
“What day of the week is the 28th?” “It's a Friday.”
He spent five days in the hospital.
She left on Thursday and came back four days later.
The baby is due (to be born) in three days.
That was the happiest day of my life.
Parenthood gets better every day.
We'll be finished in a day or two. = We'll be finished in a couple of days.
It rained for a day and a half. [=it rained for about 36 hours]
The office is closed for the day.
I call him every (single) day.
Tomorrow is another day. [=there will be more opportunities to do things tomorrow]
a day of celebration/mourning [=a day for people to celebrate/mourn]
Take one pill two times a day. [=each day]
She works eight hours a day.
It costs 10 dollars a day to park there.
The party is the day after tomorrow. = The party is in two days.
It happened the day before yesterday. = It happened two days ago.
Sometimes they didn't speak to each other for days on end. [=several days]
From that day forth/forward [=(less formally) from then on], I was determined to do better.