I might think that this applies only to those mitzvoth which obtain before entry to Eretz Yisrael, such as bechoroth (the first-born), sacrifices, and animal tithes. Whence do I derive that it applies also to those mitzvoth that apply only after entering Eretz Yisrael, such as omer, challah, the two loaves, and the show bread? From "if hearken you shall hearken to My mitzvoth" — to include the other mitzvoth.
This tells me (that they are required to learn immediately) only those mitzvoth which obtain (even) before they conquered and settled the land. Whence do I derive (the same for those mitzvoth which obtain) only after they conquered and settled the land, such as leket, shikchah, peah, terumoth, ma'aseroth, shemitah, and Yovloth? From "to My mitzvoth which I command you this day" — to include the other mitzvoth.