Midrash su Bikkurim 1:3

(Ibid. 2) "Then you shall take of the first of all the fruits of the earth": I might think that all the fruits are subject to the mitzvah of bikkurim; it is, therefore, written "of the first," and not all of the first. And I still would not know which are subject and which are not. I, therefore, reason: Communal bikkurim (the omer and the two breads) are mentioned elsewhere (viz. Vayikra 23:17), and individual bikkurim are mentioned here. Just as the communal meal-offerings, mentioned elsewhere (wheat and barley) are from the seven species, so, the individual offerings, mentioned here, are from the seven species. — But why not say: Just as there, (only) wheat and barley (are mentioned), here, too, wheat and barley! Whence are the others (of the seven species) to be derived? It is, therefore, written (Shemoth 34:26) "the bikkurim of your land," to include (all of the seven species mentioned in praise of your land). Since Scripture includes (i.e., all of the seven species) and excludes (five of them [in the instance of communal bikkurim]), you revert to the original (reasoning), viz.: Individual bikkurim are mentioned here, and communal bikkurim are mentioned elsewhere. Just as the communal bikkurim (wheat and barley) are of the seven species mentioned in praise of the land, so, the individual bikkurim are of the seven species mentioned in praise of the land. And they are (Ibid. 8:8) ("a land of) wheat, barley, grapevine, fig, and pomegranate, a land of olive-oil and honey."

"that you bring from your land": so long as they are found on the face of the land. I might think he may bring them before Shavuoth, it is, therefore, written (Shemoth 23:16) "And the feast of the harvest (Shavuoth) of the first-fruits of your work." From when do you bring? From Shavuoth until Channukah.