This is not a 24 hour day. It means the things that may happen during many years. It includes many events. God has said that he will visit this world at the end of time. It will be a time of surprise and reward. It will be a wonderful time for those who love God. But it will be a sad time for those who do not love God. Also the Bible uses the words day of the Lord to describe a terrible battle. God will use such a battle in the future to punish evil nations. Sometimes this battle is called Armageddon. The time when God will make Israel’s people free. In the New Testament, it is the time when Jesus will return. And he will start to rule on the earth.