So, a question was asked earlier: How much time passed between The Lion, the Witch, and the Wardrobe and Prince Caspian? And I had made a comment that was, rightly suggested, to ask as a question. Looking at the answers, it would appear that ~1300 years passed in Narnia with ~1 Earth year. So, how much time passed between Prince Caspian and The Dawn Treader? Earth time it seems to be ~1 year, whereas on Narnia, it seems to be ~1 year as well. I've seen the question How can the time variations be explained in the first three books of the 'The Chronicles of Narnia'? so I understand there is no direct ratio. I'm just curious as to the time difference in Narnia and Earth time between the two books.
The Voyage of the Dawn Treader itself spans many months, possibly a full year, but the time gap between the two books is stated explicitly right at the beginning of Chapter 2. This is shortly after Edmund, Lucy, and Eustace were rescued from the sea:
"Where is Eustace?" asked Lucy.
"In bed," said Edmund, "and I don't think we can do anything for him. It only makes him worse if you try to be nice to him."
"Meanwhile," said Caspian, "we want to talk."
"By Jove, we do," said Edmund. "And first, about time. It's a year ago by our time since we left you just before your coronation. How long has it been in Narnia?"
"Exactly three years," said Caspian.
I don't recall (and skimming, didn't see) as statement at the end about how long they were gone, but a few paragraphs after the above quote, Caspian does state his intent about how long they'll sail:
"Right. Well, on my coronation day, with Aslan's approval, I swore an oath that, if once I established peace in Narnia, I would sail east myself for a year and a day to find my father's friends or to learn of their deaths and avenge them if I could. These were their names: the Lord Revilian, the Lord Bern, the Lord Argoz, the Lord Mavramorn, the Lord Octesian, the Lord Restimar, and - oh, that other one who's so hard to remember."
it is 1 year of earth time between these 2 books, and about 3-4 years pass for Narnia. Timeline