In Jesus, Interrupted (HarperCollins), Bart Ehrman has this to say about the length of Jesus’ public ministry, as indicated in the canonical Gospels:

Our earliest Gospel, Mark, does not give an explicit indication of the length of Jesus’ public ministry, but does give some suggestive comments. At the beginning of Jesus’ ministry, in chapter 2, his disciples are going through the wheat fields and eating the grain, to the consternation of the Pharisees, who believe they are violating the Sabbath. This must be taking place, then, in the fall, at the time of the harvest. After this point the action moves very quickly: one of Mark’s favorite words is euthus, “immediately”—“immediately” Jesus did this, “immediately” he did that. By chapter 11, after lots of “immediately’s” we come to the last week of Jesus’ life, at the Passover feast in Jerusalem. Passover is in the spring, and the distinct impression is that the ministry has lasted a few months, from harvest time to spring.

A few months? Doesn’t everyone know that Jesus’ ministry lasted three years? Actually, the idea that it lasted three years comes not from the Synoptic Gospels—Mark, Matthew, and Luke—but from the last Gospel, John. On three separate occasions John refers to different Passover celebrations, which since they were a year apart would seem to indicate that the ministry must have lasted at least over two years, rounded up to three. But which is it? I would say this is not technically a discrepancy, but it is hard to know what to make of all of Mark’s “immediately’s” if he didn’t really mean them.

Note, then, that Ehrman’s case rests largely upon an ‘impression’ based on Mark’s use of the word ‘immediately’.

James Patrick Holding has no trouble in debunking this ‘impression’.  He also shows that it is not at all ‘hard to know what to make of all of Mark’s “immediately’s”:

Holding notes that:

1. Ehrman does not quantify his claims about Mark’s use of “immediately”.  ‘Mark uses the word “immediately” (in two related forms) 57 times; but Luke uses them 21 times, and Matthew 15 times…by Ehrman’s logic, he ought to have gotten a “distinct impression” from Matthew that Jesus’ ministry was only about a year long, and from Luke that it was perhaps two years long. Ehrman’s sense “impression” from the use of this single word is worthless.’
2. Mark never uses the word “immediately” to indicate compression of time.  Some of his uses of the work are in the context of parables (e.g. Mark 4:5, 15, 16, 17, 29, Mk 6:27).  Others indicate how quickly a person was healed by Jesus (Mk 1:31, 42; 2:12; 10:52).  Still others refer to the perception by Jesus of other peoples’ thoughts or actions (Mk 2:8, 5:30).  Then again, some are connected with the speed of an action (Mk 5:2, 6:50, 14:43).  In Mk 1:12 and v28 the word functions as marker indicating that something happened without delay.  But none of these have any bearing on the length of Jesus’ public ministry.

Is Bart Ehrman being incompetent, dishonest, or just careless?

You decide.