What does the Torah mean when it describes the seven years as "Yamim Achadim" (which seemingly clashes with human nature)?
Rashi: Refer to 29:18:1:1.
Riva #2: After he finished working, it felt that it was a small toil, for he loved her so much. 3
Malbim #2: One who loves amidst desire, to fulfill his pleasure, he loves himself; a day feels like a year. Yaakov loved her (virtuous deeds), therefore it felt like a few days.
Ha'amek Davar (to 29:18): He understood that "Yamim Achadim" is seven years. Due to his love for her, he thought that they need not be full years, so he said "Sheva Shanim," i.e. until Rosh Hashanah of the seventh year. He did not say "Shavu'a Shanim," which would be seven full years from day to day.
Ner Uziel (p. 174): Time drags when one feels ready, and merely waits until he gets his desire. Each day separates him from his desire. Yaakov realized that he needs to perfect himself more before he is ready to marry Rachel and fulfill his mission. 4 Each day brought him closer to his goal.
Bechor Shor: This explains why Yaakov did not suggest a shorter time. He thought that he was underpaying!
Which is why the Torah adds "in his love for her" - because love causes a person to act and to think irrationally (Seforno).
Pane'ach Raza: However, while working, surely it felt like a long time.
What is the significance of the Torah's constant repetition of the fact that Yaakov loved Rachel?
Oznayim la'Torah: In order to clarify that, when the Torah will mention his hatred of Leah, it is only relative to his love of Rachel. 1 In other words, although he loved Leah like a man loves his wife, only when compared to his love of Rachel, it is considered hatred. 2
Why does it say that he worked "b'Rachel"?
Ohr ha'Chayim: He publicized at the time of Avodah that he is working for Rachel, and she is in exchange for his work. This way it would not be forgotten, and Lavan could not deny and say that it was for Leah.