The day of Jehovah is coming, for it is near, a day of darkness and thick darkness, a tiny of cloud and gloom, as has never happened of old, nor will be again after it through the years of generation after generation. Joel 2:1-2, 11.
Here 'day' stands for a state of darkness, thick darkness, cloud and gloom - a state of individuals in particular and of all in general. In Zechariah,
I will remove the iniquity of this land in a single day. On that day you will shout, each to his companion, under his vine and under his fig tree. Zechariah 3:9-10.
And elsewhere in Zechariah,
There will be one tiny, it is known to Jehovah, which is neither day nor night, and at evening time there will be light. Zechariah 14:7.
State is clearly meant here, for it is said that 'it will be a day, which is neither day nor night; at evening time there will be light'. The same meaning is also clear from the following in the Decalogue,
Honour your father and your mother, that your days may be prolonged, and that it may be well with you in the land. Deuteronomy 5:16; Deuteronomy 25:75.
Here 'a prolonging of days' does not mean living on into old age but a state that is happy.
 In the sense of the letter 'day' cannot be seen to mean anything other than a period of time, but in the internal sense it means a state. Angels, who abide in the internal sense of the Word, do not know what a period of time is, for the activity of the sun and moon with them does not produce divisions of time. As a consequence they do not know what a day or a year is, but only what states and changes of state are. This is why among angels, who abide in the internal sense of the Word, anything connected with matter, space, and time, goes unnoticed, as with the following usages in the sense of the letter in Ezekiel,
The day is near, even the day of Jehovah is near, a day of cloud; it will be a time of the nations. Ezekiel 30:3.
And in Joel,
Alas for the day! For the day of Jehovah is near, and as destruction. Joel 1:15.
Here 'a day of cloud' stands for cloud or falsity, 'a day of the nations' for the nations or wickedness, and 'the day of Jehovah' for vastation. When the concept of time is removed there remains the concept of the state of the things existing during that period of time. The same applies to the days and the years that are mentioned so many times in this chapter.