Rav Chaim Pinchas Scheinberg zt”l (Rabbeinu Yonah on Avos, with He’oras U’Biurim pg. 57) and the Admor of Sanz, the Shefa Chaim zt”l (Divrei Torah, Year 9, gilyon 22), among others, noted the painful irony of the fact that the bein hazmanim of Av falls precisely at the moment the Gemara (Taanis 31a) identifies as the season of Torah intensification.
The Gemara teaches: מכאן ואילך דמוסיף יסיף דלא יוסיף תקבריה אמיה. Rashi explains this to mean: מחמשה עשר באב ואילך, דמוסיף לילות על הימים לעסוק בתורה יוסיף חיים על חייו. דלא יוסיף לעסוק בתורה בלילות. תקבריה אימיה כלומר ימות בלא עתו. — “From Tu B’Av onward — whoever adds nighttime hours to daytime hours for Torah study adds life to his life. Whoever does not add nighttime hours to his Torah — his mother will bury him, meaning he will die before his time.”
Rabbeinu Gershom (Bava Basra 121b) explains that the great Yom Tov of Tu B’Av is the fact that from that date and on the cutting of wood for the mizbe’ach ceased, which meant that people had more time to learn Torah.
Rav Yonasan Eibshitz zt”l writes in Yaaros Devash (1:4): הנה ימים באים ימי חפץ ומט“ו באב ואילך הגיע זמן הוספה להוסיף אומץ בתורה ויראת ד‘ חזקו ואמצו לבבכם בתורת ד‘, ואין לנו שיור רק התורה הזאת. “Behold, days of longing are coming — from Tu B’Av onward the time has arrived to add strength in Torah and fear of Hashem. Be strong and take courage in the Torah of Hashem, for we have nothing left but this Torah.”
The truth is, that because of the above the yeshivos of Ger, Tchebin, Nezer HaTorah, and others begin Elul zman on Tu B’Av.
Strictly speaking the above Gemara doesn’t apply today. We can bring proof from the Magen Avraham cited by the Mishnah Berurah (131 s.k. 30). The Magen Avraham says: We don’t recite tachanun, as it was a great Yom Tov “in the times of the Beis HaMikdosh.” Implied is, that in the times of the Beis HaMikdosh it was a great Yom Tov, but not today. The reason it would no longer apply today is because we don’t cut wood for the marocha anymore. Additionally, the natural lengthening of the night no longer changes our learning habits like it did in earlier times, when the additional darkness literally extended the available hours for Torah learning.
