Consider: how much introducing of the world did Tolkien provide in The Hobbit? To give but one example.
Actually, quite a lot. For instance he spends about a page near the beginning of the book telling us what a hobbit
is and a bit of Bilbo's family history. And besides that, he's not writing about a world that isn't Earth. It's Earth in a far, far distant era of the past. Which means there are a lot of things he doesn't
need to explain. The animals, the plants, the foods ... usually, he needs only to identify them and readers require no explanations.
But I think that if the setting of a story is
not Earth the author should establish that pretty early, if at all possible. How awkward it would be to discover two or three chapters in that it was another world or planet (unless the author had a particular, and particularly good, reason for keeping it a secret). But there are countless different and quick ways to do that, like unfamiliar-sounding names of the people or important places. Or a glance at the sky showing extra suns or moons. A glimpse of a calendar where the the months of the year are unfamiliar or the length of a week is different.
Handled well, small clues can suggest a great deal that readers can figure out for themselves, so the author doesn't have to explain those things for them.
But that presumes a world that is still fairly Earth-like. Because the more exotic the setting—the flora, the fauna, the human or humanoid inhabitants, the weather and terrain, perhaps even the physics—the more that things like politics and wars and unknown magics and religions (previously unknown to the reader, that is) figure in the plot, the more and sooner the author is going to have to do some explaining. Though it need not always come in chunky and clunky info dumps. In fact, the sooner the writer starts dribbling in important bits of information, the less will have to be delivered all at once in a lump when it can no longer be avoided. Nor need longer explanations, if needed, necessarily be boring. In the right hands, they can be quite entertaining.