And it is related in the book "Ha-Shakdan" (vol. 2, p. 240) that one of Ha-Rav Yosef Shalom Elyashiv's grandsons once asked him why he does not stay awake all night on Shavuot like everyone else, but follows his regular learning schedule of waking up at 2:00 AM to learn Torah… Rav Elyashiv explained that he calculated that if he changed his few hours of sleep on that night, he would not gain more time to learn Torah, and he would actually lose 15 minutes of learning! For a few precious minutes of learning Torah, he decided that it is preferable to go to sleep at the beginning of the night as usual…

And Gerrer Chasidim have a saying: Our Tikun Leil Shavuot is Keriyat Shema Al Ha-Mita (reciting the Keriyat Shema before going to bed)…