It is written:
“But woe to those who are pregnant and to those who are nursing babies in those days!” (Matthew 24:19)
“And unless those days were shortened, no flesh would be saved; but for the elect’s sake those days will be shortened.” (Matthew 24:22)
“”Immediately after the tribulation of those days the sun will be darkened, and the moon will not give its light; the stars will fall from heaven, and the powers of the heavens will be shaken.” (Matthew 24:29)
As the Lord preached about the impending destruction of the city of Jerusalem, His Apostles asked Him three important questions: when will these things be, what will be the sign of Your coming, and what will be the sign of the end of the age (Matthew 24:3)?
While Mark and Luke deal primarily with the destruction of the city of Jerusalem (which occurred in 70 A.D.), Matthew also deals in great detail with the “sign” of the end of the world (age).
In Matthew 24, at which point did Jesus switch from talking about the destruction of Jerusalem to talking about the Second Coming? One clue lies in the phrase “those days” verses the Day.”
When referring to the destruction of the city of Jerusalem in Matthew 24, Jesus used the phrase “these days.” However, when He began talking about the Second Coming, Jesus used the phrase “that day and “the day.”
“By the very nature of the case, the numerous events leading up to the Roman military destruction of the temple in AD 70 will require a number of days. Hence, in the portion of his Discourse prior to Matthew 24: 36 Jesus mentions “those days [plural]” (v 19, 29) and even comforts his disciples by noting that “those days” will be “cut short” (v 22). This mention of the days of the tribulation period are set in stark contrast to the singular day —indeed, the exact moment —of the second coming: “But of that day and hour no one knows, not even the angels of heaven, nor the Son, but the Father alone” (Matt 24: 36). After this transition at 24: 36 he repeatedly mentions the singular “day” (24: 42, 50) or “the day” and “the hour” (25: 13). The second advent does not involve a series of historical actions, as is the case with the Roman military operations against the Jews, Jerusalem, and the temple. The second advent is a one-time, catastrophic event conducted by a singular individual, Christ himself.” (Ken Gentry, The Olivet Discourse Made Easy, 2546-2555 (Kindle Edition); Draper, VA; The Apologetics Group)
In Matthew 24, Jesus began talking about “the Day” (i.e., the Second Coming) in verse 36. Thus, Matthew 24:4-35 dealt with the destruction of Jerusalem.