Tosafos discusses why Birchas HaTorah can work once in the morning and one is not required to make the bracha again for the duration of the day. Tosafos makes this point by contrasting Birchas HaTorah to Leishev BaSuccah which is required every time one returns to eat in the succah. Tosafos explains that eating in the succah has set times therefore the bracha that is being made only goes on the specific meal and whatever sitting in the succah follows it. However, by Torah there is a mitzvah to learn constantly - והגית בו יומם ולילה, therefore even if one has breaks throughout the course of the day, they would not be required to say birchas hatorah when they return to their learning. The point that Tosafos is trying to make is more clearly brought out by Rabbeinu Yona. Rabbeinu Yona suggests that there should be a distinction between different types of people. Those who learn regularly throughout the day would only need to make birchas hatorah once since their intent when making the bracha goes on the entire day since they will spend the majority of it learning. However, those who aren't spending most of their day learning is only making a bracha on what he is about to learn, therefore when the opportunity arises that he is unexpectedly able to learn, he should need to make a new birchas hatorah. To that Rabbeinu Yona responds that the minhag is that even those who fall in the second category do not make a new birchas hatorah. The rationale is:
דכיון דמצות הקריאה כל היום היא, אותה הברכה שבבקר פוטרת כל מה שיקרא ביום
Rabbeinu Yona (citing the R"I) originally thought that the birchas hatorah is dependent on whether a person is actually spending his day learning and only one who does, would be able to make the bracha only on the morning. However, he justifies the minhag based on the fact that the obligation to learn all day applies to everyone. In short, the reason we don't consider the time one is not learning to be a hefsek is because the obligation is to learn even during those times. This is the intent of Tosafos as well to differentiate between birchas hatorah and the bracha on succah. It isn't dependent on what one does, rather on the inherent obligation.
The Tzlach writes what even he considers to be a tremendous chiddush and wonders why this isn't pointed out by rishonim and other acharonim. Although we hold that woman are entitled to make birchas hatorah as the shulchan aruch paskens in the last si'if of 47, the rationale of Tosafos that we don't regard the break time to be a hefsek because they are obligated to learn even during those times, doesn't apply to women. Women are not obligated at all to learn. Therefore, if a woman makes birchas hatorah in the morning and then returns to learn later in the evening, she would need to make a new birchas hatorah.
It seems to me that this chiddush may be dependent on how exactly we justify a woman's right to make birchas hatorah. The Biur Halacha quotes two approaches. The Beis Yosef and Magen Avrohom write that a woman can make birchas hatorah since they are required to learn laws that are pertinent to them and also obligated to say the parshiyos of korbanos. This is what the birchas hatorah goes on. The Gr"a disagrees and says that it is like every time bound positive mitzvah that they have a right to make a bracha on. The Biur Halacha suggests that according to the first approach, they can technically be motzi a man in birchas hatorah, whereas according to the approach of the Gr"a, they cannot. Perhaps another distinction is that although the rishonim discuss whether one needs to learn immediately after making birchas hatorah (even the yerushalmi may only require this by ahava rabba), our custom is to say pesukim and a mishna right after birchas hatorah. It would seem logical that one would need to learn something that they are obligated to learn, so that the birchas hatorah can go on that learning. Based on the approach of the gr"a women can learn anything after birchas hatorah, including the saying of the pesukim and mishna that we say. But according to the first approach, they would need to learn halachos that apply to them.
Perhaps another distinction between these two approaches is the suggestion of the tzlach. Do we consider the time in between the learning to constitute a hefsek. If they are making birchas hatorah due to their requirement to learn halachos that are pertinent, just as we don't consider the time in between a hefsek for men, we shouldnt consider it a hefsek for women either. But if they are only able to make a birchas hatorah as they make a bracha on every time bound mitzvah, the time in between the learning should be a hefsek for them and require them to make a new birchas hatorah when they come back to learn, as the tzlach suggests.