When did the fig tree wither?

 Matthew 21:19–21 NIV

Seeing a fig tree by the road, he went up to it but found nothing on it except leaves.

Then he said to it, “May you never bear fruit again!” Immediately the tree withered.

20 When the disciples saw this, they were amazed. “How did the fig tree wither so quickly?” they asked.

21 Jesus replied, “Truly I tell you, if you have faith and do not doubt,

not only can you do what was done to the fig tree, but also you can say to this mountain,

‘Go, throw yourself into the sea,’ and it will be done.

Mark 11:19–20 NIV

When evening came, Jesus and his disciples[a] went out of the city.

20 In the morning, as they went along, they saw the fig tree withered from the roots.

21 Peter remembered and said to Jesus, “Rabbi, look! The fig tree you cursed has withered!”

Matthew 21:19–21indicates the fig tree Jesus cursed withered immediately. However, Mark 11:19–20 would suggest the fig tree withered some time later. So, which is it? It takes a careful reading of the sequence of events to resolve this apparent contradiction. We will start with Mark 11 as it is the more complete version. Note that Jesus and his apostles visit Jerusalem on three consecutive days:

Visit 1 (Mark 11:1–11)

Jesus and the disciples come to Bethphage and Bethany, at the Mount of Olives, on the way to Jerusalem.

Jesus enters Jerusalem on a donkey.

In the evening, they return to Bethany for the night.

Visit 2 (Mark 11:12–19)

They leave Bethany in the morning.

They comes upon Fig tree and Jesus curses it.

They return to Jerusalem and Jesus cleanses temple.

In the evening, they leave the Jerusalem.

Visit 3 (Mark 11:20–33)

In the morning, they head back to Jerusalem and pass withered fig tree.

Peter remembers Jesus cursing the fig tree.

Jesus returns to temple in Jerusalem and is challenged the priests and elders.

Now, onto the Matthew account and you should spot the differences:

Visit 1 (Matt 21 1:1–17)

Jesus and the disciples come to Bethphage, at the Mount of Olives, on the way to Jerusalem.

Jesus enters Jerusalem on a donkey and clears the temple.

They leave Jerusalem and head to Bethany for the night.

Visit 2 (Mat 21:18–46)

The next morning, returning to Jerusalem, Jesus curses fig tree amazing the disciples amazed how quickly it withered.

Jesus returns to the temple in Jerusalem and is challenged by the priests and elders.

Notice that the Matthew account is missing some important details. It explicitly mentions two separate visits to Jerusalem but doesn't mention the third. Instead, it merges the events of the three visits over the two visits to Jerusalem that's mentioned. The Mark account, on the other hand, gives a more clear description of events. Jesus curses the fig tree on one day, and Peter (and the apostles) remark about it the next day.

As an aside, there are two Greek words used for "immediately" in Matthew 21:19 depending on which underlying text is used, mēketi and parachrēma. Parachrēma implies "immediately" or "at once" while mēketi means "no longer" or "not anymore." Given the proper context of Mark 11, it's likely the latter.

Did Matthew get it wrong? Dealing with Matthew 27:9–10

Matt 27:9 Then was fulfilled what was spoken by Jeremiah the prophet, saying, “And they took the thirty pieces of silver, the value of Him who was priced, whom they of the children of Israel priced,

Matt 27:10 “and gave them for the potter’s field, as the LORD directed me.”

Here, Matthew seems to mistakenly attribute the story of the purchase of the potters’ field to Jeremiah rather than Zechariah. How is it possible that Matthew made such a glaring mistake? In dealing with apparent contradictions, it's been my experience that there's always plauseable explanations to be found, even if it's impossible to know the definitive answer. So, let's examine Matthew 27:9–10.

Upon careful inspection, Matthew 27:9 quotes Zechariah 11:12-13:

Zec 11:12 Then I said to them, “If it is agreeable to you, give me my wages; and if not, refrain.” So they weighed out for my wages thirty pieces of silver.

Zec 11:3 And the LORD said to me, “Throw it to the potter”—that princely price they set on me. So I took the thirty pieces of silver and threw them into the house of the LORD for the potter. (NKJV)

However, Matthew 27:10 alludes to Jeremiah 32:6-9:

Jer 32:6 And Jeremiah said, “The word of the LORD came to me, saying,

Jer 32:7 ‘Behold, Hanamel the son of Shallum your uncle will come to you, saying, “Buy my field which is in Anathoth, for the right of redemption is yours to buy it.” ’

Jer 32:8 “Then Hanamel my uncle’s son came to me in the court of the prison according to the word of the LORD, and said to me, ‘Please buy my field that is in Anathoth, which is in the country of Benjamin; for the right of inheritance is yours, and the redemption yours; buy it for yourself.’ Then I knew that this was the word of the LORD.

Jer 32:9 “So I bought the field from Hanamel, the son of my uncle who was in Anathoth, and weighed out to him the money—seventeen shekels of silver.

Zechariah mentions thirty pieces of silver and a potter, but nothing about buying a field. Jeremiah, on the other hand, visits a potter's house (Jer 18), buys a potter's jar and smashes it in the Valley of Slaughter (Jer 19), and then buys a field from his cousin Hanamel for seventeen shekels of silver (Jer 32) (makes you wonder if Hanamel was a potter). Zechariah's prophecy and Jeremiah's actions both foreshadowed the death of Judas. So, Matthew 27:9–10 seems to be an amalgamation of Zechariah and Jeremiah. For reasons that are not clear, Matthew attributed it solely to Jeremiah, perhaps because Jeremiah preceded Zechariah.

On a side note, the Old Syric translation of Matthew 27:9 (circa 5th century) doesn't mention Jeremiah or Zechariah but simply says, "Then was fulfilled what had been spoken by the prophet, who said, And I took the thirty (pieces) of silver, the price of him who was precious, whom the sons of Isroel bargained for." Make of that what you will.

There is something called "citation formula" (sometimes quotation formula) or "ascription." It's basically a literary device where a writer may attribute a quote or idea to someone else. For example, in Stephen's speech in Acts 7, he appears to blend or summarize several Old Testament passages. In Acts 7:42–43, Stephen attributes a statement about Israel's idolatry to the book of Amos. However, the wording closely resembles a passage from the book of Isaiah (Isaiah 66:17). I believe this is what Matthew was doing. He was quoting Zacheriah, but doing it within the larger context of Jeremiah. The Apologetics Team website gives an excellent explanation. Excerpts: 

What then is the solution? It would appear that, while quoting primarily from Zechariah, Matthew was pointing the reader to a key passage (or theme) in Jeremiah as well, one that tied in with the point he wanted to make. Thus, to draw this to the reader’s attention, he made reference to Jeremiah, since the reference to Zechariah would be obvious...

It would seem then, in light of all the potential texts in Jeremiah, that Matthew was most likely pointing to Jeremiah 19:1–13, where the prophet is commanded by the Lord to “buy a clay jar from a potter” (yotser) and to take it, in the presence of the elders and the priests, “to the Valley of Ben Hinnom, near the entrance of the Potsherd Gate,” proclaiming a word of solemn judgment on Jerusalem: “This is what the Lord Almighty, the God of Israel, says: Listen! I am going to bring a disaster on this place that will make the ears of everyone who hears of it tingle” (19:1–3). Jeremiah was then to smash the potter’s jar and say: “This is what the Lord Almighty says: I will smash this nation and this city just as this potter’s jar is smashed and cannot be repaired” (Jer. 19:11). —Matthew 27:9–10 prophecy from Zechariah or Jeremiah?

On another side note, The Greek Septuagint, the one New Testament authors often quote from, doesn't mention anything about a potter in Zechariah 11:13. It only says, "And the Lord said to me, Drop them into the furnace, and I will see if it is good , as I was proved for their sakes. And I took the thirty pieces of silver, and cast them into the furnace in the house of the Lord." So, while Matthew 27:9 does quote Zechariah, it's reasonable to conclude Matthew 27:10 is a reference to Jeremiah 32:6–9, as Zechariah's prophecy doesn't mention anything about purchasing a field.