I'm starting a Bible study on the Gospel of John tomorrow, so I've been mugging up the book. Today, I was outlining the whole thing (first step in the good ol' Inductive Bible Study method), and I spent a fair amount of time after that trying to get the chronology straight. John marks the passage of time by structuring his narrative around a lot of feasts.
In John 2:13, he says the Passover was "at hand," meaning in a few days. This is a "few days" after the wedding at Cana, which was the third day after John pointed out Jesus as the Lamb of God that takes away the sin of the world. That event is not Jesus's baptism; Jesus seems to have returned from the wilderness (40 days' temptation), plus had a few days to get his own digs in Capernaum. So, allowing for 40 days of temptation, plus a few days at least to find a place to live, plus a few more days of gathering up disciples, plus a few days and the Passover is just around the corner means my best guess was that Jesus couldn't have been baptized any later than, say, January 20-25.
Of course, he could have been baptized much earlier -- say, around the previous Rosh Hashanah or Yom Kippur. He might have spent several weeks settling his Mother's care, etc., before taking off to figure his call out. So, let's say he was baptized sometime between, oh, September 15 and January 15, just for grins.
And there is this ancient commemoration on or shortly after January 6. Spooky. Somebody's done this set of calculations before, I think. The Epiphany isn't just an arbitrary, "made-up" festival to give the faithful a happy holiday in the bleak midwinter. No doubt many traditions coalesced around Christmas and Epiphany, but things weren't just drug in from anywhere. The thing hangs together in a pleasing fashion, and no great violence is done to the chronology, either.
Traditionally, Jesus had 3 years of ministry. If we start with mid-winter, we can count three Passovers in John's gospel. The first is associated with the cleansing of the Temple. The second is out in the boonies, but contains the feeding of the five thousand and Jesus's teaching on the bread of life vis-a-vis the manna in the wilderness. The third is right after his triumphant entry.
So, two and a half years of ministry. Close enough.
BTW, the unnamed "Festival of the Jews" mentioned in 5:1 looks like either Rosh Hashanah or Yom Kippur to me. Rosh Hashanah celebrates the creation of the world, and would be an apposite time for Jesus to say, "my Father is working still, and so am I" (5:17). On the other hand, Yom Kippur is the time of atonement and judgment, and Jesus's teaching is all about judgment in 5:22-29.
* To coin a phrase. *cough-cough*