The phrase "exciting day" is correct and usable in written English. You can use the phrase to describe a day that is particularly interesting or stimulating, either as part of a sentence or as a standalone phrase. For example, "Today is shaping up to be an exciting day. I can't wait to see what new adventures the day holds!".
Tomorrow will be an exciting day.
It's an exciting day, every day".
"It is an exciting day ahead.
Today was an exciting day at Cherry Ann Park!
This is an exciting day at MIT Technology Review.
"It's going to be a pretty exciting day," Rodriguez said.
This is a very exciting day for the Buffalo Bills".
Let's look back at his exciting day of constant apologizing.
They'd be waking up to a more exciting day.
"It is going to be an exciting day".
That was an odd, yet very exciting day for us.
I love the desktop app, it’s always running on my Mac. Ludwig is the best English buddy, it answers my 100 queries per day and stays cool.
Cristina Valenza
Retail Lead Linguist @ Apple Inc.