Did the tree that Jesus cursed wither
 immediately or overnight?
  Matthew 21:19 and Mark 11:14,20

1. Immediately (Matthew 21:19) - "Seeing a lone fig tree by the road, He came to it and found nothing on it except leaves only; and He said to it, "No longer shall there ever be any fruit from you." And at once the fig tree withered.

2. Overnight (Mark 11:14,20) -  "He said to it, "May no one ever eat fruit from you again!" And His disciples were listening. . .²⁰As they were passing by in the morning, they saw the fig tree withered from the roots up."

     This "contradiction" is one of the more problematic.  If you look at the chart below you will see that that the areas in blue are difficult to reconcile if we look at them in a strictly chronological manner.   One answer I have discovered says that Matthew writes thematically, often grouping topics together without a detailed focus on chronology, where Mark does not.  In other words, Matthew simply compressed the event to a single instance in order to make the point about the necessity of bearing fruit.  Therefore, Matthew's account is not meant to be chronological, but thematic and that it is Mark's account that presents the chronological order.  This is certainly a possible solution.  However, the weakness of this answer is in Matthew's use of the phrase "at once the fig tree withered" in 21:19.  If Matthew's account is not intended to be chronologically precise, that is one thing that I can accept since it does indeed occur in Matthew.  But, the phrase which tells us the fig tree withered "at once" is stating it was immediate.  This doesn't leave much room for the fig tree to wither overnight.  But, if Matthew were compressing the incident, then the immediacy would be evident. 
     Another possibility is that there are two different fig trees that were cursed.  I don't think this is a viable option if you look at the chart below.  But it is a possibility.
     Yet another possibility is that in Matt. 21:19, it is not said how much the tree withered.  It could be that the tree showed immediate signs of withering but had not completely withered.  Then, in Mark 11:14,20 the next morning the disciples saw that the tree had withered from the root up.  In other words, the withering was complete.
     Jesus was obviously using the Fig Tree as a symbol as He taught.  His condemnation of the fig tree for not bearing fruit is actually a condemnation upon the Jewish leadership and their spiritual deadness.  Note the context of Christ cleansing the temple (Mark 11:15-17) and His quote from Isaiah 56:7 and Jer. 7:11.  The fig tree was used elsewhere in scripture symbolically for leaders (Judges 9:10-11), fortifications (Nahum 3:12), in parables (Matt. 24:32ff), etc.  If Jesus were using the Fig Tree as a symbol, then either Matthew or Mark could easily take liberties in focusing on the issue of the meaning of the story rather than recounting a chronological event.  
     Nevertheless, the account does pose a challenge to the doctrine of inerrancy.  But, does this mean that the Bible is not trustworthy or not inspired?  Not at all.  We do not give up on physics or mathematics or astronomy if we find things we cannot easily explain.  The Bible is a wondrous and beautiful book and it will always stand the test of time.  As archaeology continues and older and better manuscripts are found, then, as has happened in the past, more and more biblical discrepancies will be answered.
  

    All scripture quotes are from the NASB.