Birkot HaTorah are recited in the morning in conjunction with the recital of Birkot HaShachar, and they encompass all learning performed throughout that day. Even if a person goes to eat and to work afterwards, he does not need to recite Birkot HaTorah upon returning to learn.
In that respect Birkot HaTorah differ from other Birkot HaMitzvot (berachot recited upon the performance of a mitzvah). Concerning all other mitzvot, every time a person performs the mitzvah anew, he must recite another berachah because the mitzvot are only designated for a specific time of the day, or for a particular act. For example, the mitzvah of sukkah requires that a person eat and sleep in the sukkah, while at all other times he is permitted to go wherever he desires. Similarly, the mitzvah of tallit can be fulfilled after one minute of the day. Therefore, every time one wraps himself anew in his tallit, or goes into the sukkah to eat another meal, he must repeat the particular berachah intended for that mitzvah.
However, the mitzvah of learning Torah is a general mitzvah that encompasses all of a person’s days and hours, as it is written (Joshua 1:8), “You shall meditate thereon day and night.” Even if a person learned in the morning, the commandment to learn still applies at night and at every available hour (Tosafot, Berachot 11b, s.v. “Shekvar”). Further, even when a person is not learning Torah, the Torah guides his life within the confines of halachah, middot (proper character traits), and faith. Even when a person is relieving himself or bathing, times at which it is prohibited to think Torah thoughts, there are halachot guiding him in these instances also, thus illustrating that no one can ever detach himself from Torah (see Agur, section 1, brought by the Beit Yosef 47:11). Therefore, Birkot HaTorah recited in the morning cover all of one’s learning throughout that day, and any work or business conducted in the interim is not considered to be an interruption (Shulchan Aruch 47:10).