Concerning the time of the end, Matthew 24:22 states:

And unless those days were shortened, no flesh would be saved; but for the elect’s sake those days will be shortened. NKJV

If those days had not been cut short, no one would survive, but for the sake of the elect those days will be shortened. NIV

There is a parallel verse in Mark 13:20.

And unless the Lord had shortened those days, no flesh would be saved; but for the elect’s sake, whom He chose, He shortened the days. NKJV

If the Lord had not cut short those days, no one would survive. But for the sake of the elect, whom he has chosen, he has shortened them. NIV

In quoting from Isaiah, Romans 9:28 states a similar thing:

FOR HE WILL FINISH THE WORK AND CUT IT SHORT IN RIGHTEOUSNESS, BECAUSE THE LORD WILL MAKE A SHORT WORK UPON THE EARTH.” NKJV

For the Lord will carry out his sentence on earth with speed and finality. NIV

What do these verses mean by the days being “cut short” or “shortened”?

The Bible gives a specific length of time for various end time events.  Here are some examples.

The time of great trouble at the end will last for a time, times, and half a time, which generally understood to be 3½ years. 

Dan 12:1  “At that time Michael shall stand up, The great prince who stands watch over the sons of your people; And there shall be a time of trouble, Such as never was since there was a nation, Even to that time. And at that time your people shall be delivered, Every one who is found written in the book.

Dan 12:7  Then I heard the man clothed in linen, who was above the waters of the river, when he held up his right hand and his left hand to heaven, and swore by Him who lives forever, that it shall be for a time, times, and half a time; and when the power of the holy people has been completely shattered, all these things shall be finished.

The holy city (Jerusalem) will be trampled underfoot for 42 months (which is 3½ years).

Rev 11:2  But leave out the court which is outside the temple, and do not measure it, for it has been given to the Gentiles. And they will tread the holy city underfoot for forty-two months.

The two witnesses preach for 1,260 days (which is about 3½ years).

Rev 11:3  And I will give power to my two witnesses, and they will prophesy one thousand two hundred and sixty days, clothed in sackcloth.”

The beast is given authority to exist for 42 months (which is 3½ years).

Rev 13:4  So they worshiped the dragon who gave authority to the beast; and they worshiped the beast, saying, “Who is like the beast? Who is able to make war with him?”
Rev 13:5  And he was given a mouth speaking great things and blasphemies, and he was given authority to continue for forty-two months.

The length of these events has been set by God.  God is not going to shorten (or lengthen) them.  Which brings us back to the question, what does it mean in Mat 24:22 and Mark 13:20 for “those days” to “cut short” or “shortened”?

Mat 24:22 And unless those days were shortened [koloboo], no flesh would be saved; but for the elect’s sake those days will be shortened [koloboo].

Mar 13:20 And unless the Lord had shortened [koloboo] those days, no flesh would be saved; but for the elect’s sake, whom He chose, He shortened [koloboo] the days.

The Greek word koloboo appears nowhere else in the Bible except in these two verses, so we can’t look at other Scriptures to see how koloboo is used.  According to Thayer’s Greek Definitions, koloboo can mean, mutilate, shorten, abridge, curtail.  And according to Strong’s, koloboo can mean, dock, abridge, curtail.  So there is nothing wrong with the translations. 

If we view the shortening in the context of the prophecies in Daniel and Revelation which set a specific time-period of 3½ years, then the meaning becomes clear.  God has already shortened the days to 3½ years; the shortening of days is baked into the prophecies.  God is letting us know that world conditions will become so dire that no flesh would be saved if He didn’t intervene after 3½ years.

What about Romans 9:28?

Rom 9:28 FOR HE WILL FINISH THE WORK AND CUT IT SHORT [suntemno] IN RIGHTEOUSNESS, BECAUSE THE LORD WILL MAKE A SHORT [suntemno] WORK UPON THE EARTH.”

The Greek word suntemno appears nowhere else in the Bible except in this one verse, so we can’t look at other Scriptures to see how suntemno is used.  According to Thayer’s Greek Definitions, suntemno can mean, cut it pieces, cut short, finish quickly, hasten.  And according to Strong’s, suntemno can mean, do concisely (speedily), cut short. 

Is God going to cut short His work and not do a complete work?  There are no other Scriptures which indicate this.  Surely a better translation of suntemno is “quickly” which is what many translations have.  For example:

For the Lord will carry out his sentence on earth with speed and finality. NIV

FOR THE LORD WILL EXECUTE HIS WORD ON THE EARTH, THOROUGHLY AND QUICKLY.” NASB

Conclusion

The days being “cut short” or “shortened” in Matthew 24:22 and Mark 13:20 should be understood in the context of the prophecies of Daniel and Revelation which set the length of end time events.  The shortening of the days has already happened and is baked into the prophecies.

The work being “cut short” or “shortened” in Romans 9:28 is better translated as “quickly”.