If you follow that phrase in the Bible, you will discover that day is a time of wrath, judgment, and retribution toward mankind. I have no doubt that it refers to a future time of tribulation that will come upon the earth in a future day. As I understand the Word of God, I see that day covering especially the last 3 years of the tribulation period, or the time of Jacobs trouble. The reality of things is that it is not the kind I see in the latter chapters of the Revelation. Peace is taken from the earth.
Famine comes upon the earth.
The rider on pale horse comes- death covers the earth. There is a martyred remnant crying with a loud voice. Sixth Seal- Anarchy comes upon the earth. Sun becomes back as sackcloth, moon becomes as blood, stars of heaven fall to the earth, and heaven depart as a scroll, and people cry for the rocks and mountains to fall upon them, to keep them from the wrath of the Lamb. Great mountain burns with fire and is cast into the sea.