The phrase "a day of intense" is correct and usable in written English.
It can be used to describe a day characterized by strong emotions, activities, or experiences.
Example: "After a day of intense meetings and discussions, I felt completely drained by the evening."
Alternatives: "a day of extreme" or "a day of heightened".
Mr. Silver's announcement capped a day of intense budget negotiations.
The announcement from Mr. Arafat's office followed a day of intense politicking within Fatah.
The vote to recess followed a day of intense politicking and strategizing by supporters of same-sex marriage.
The Ranger operations began after a day of intense bombing, including attacks near Kandahar, that continued even though Friday is the Muslim holy day.
The issue of Kiev's gas debts appeared not to have been resolved despite three meetings between Putin and Poroshenko in a day of intense diplomatic activity.
His speech at Columbia, in advance of his planned speech today at the United Nations, produced a day of intense protests and counterprotests around the campus.
He spoke after an day of intense talks, described as preparations for an Oct. 25 summit meeting in Texas between President Bush and President Jiang Zemin.
Likewise, previous studies have indicated that an hour a day of moderately intense exercise is more effective at preventing heart disease than half an hour.
This was not a day of high-intense drama but no one who witnessed it could complain as Marcus Trescothick, for the second time in six days, cut, drove and pulled his way to a magnificent century and then on to a double century.
After a failed day of intense politicking, with a devastating majority of the Parliament lined up to bring him down, Mr. Barak did not even wait for the lawmakers to vote him and themselves out of office.
In a second day of intense bombardment of Gaza and a continuing barrage of rocket fire into Israel, sirens were activated in Tel Aviv for the first time since the 1991 Gulf war to warn residents to take shelter.
