Q. Dear Rabbi
Since on Rosh Hashana we are being judged during the first three hours of the day which begin around 5.30 AM, would not davening vesikin (with the sunrise) be the best alternative, rather than spend that time sleeping in bed as most people do?

A. The Talmud (Avoda Zarah 3b – 4a) quotes disagreeing opinions as to what Hashem does during the first three hours of the day. Rav Yehuda in Rav’s name maintains that the first three hours are spent in Torah learning while the next three are dedicated to judgment, while on daf 4a the Talmud quotes in the name of Rav Yosef that a person should not pray Musaf during the first three hours of the first day of Rosh Hashana since it is a time of resulting in anger. The Talmud mentions that this may disagree with the previous opinion and now we maintain that the first three hours are dedicated to judgment that harbors anger. Kerem Hatzvi (quoted in Talelei Oroth p.43) explains that this is the reason why the piyut “L’Ei-l Orech Din” is recited the first day during shacharis, while on the second day it is said at musaf
Ya’aros Devash (part 1, drush 14) adds another insight. He maintains that during the common days of the year the judgment for that day is written and signed before the end of the first three hours, so one should preferable pray then, since what point is there in davening after the judgment has been sealed. Not so on Rosh Hashana when the sentence is not signed yet. See also Shulchan Aruch and Mishna Berura 591: 8 that the judgement of Rosh Hashana is far more serious, severe and of consequence than the daily due process.
Horav Shlomo Miller’s Shlit’a opinion is that indeed if someone can muster his concentration and intention, he should pray vasikin, if not he should spend at least part of that time learning Torah. He mentioned that some assert that the saying (Yerushalmi quoted by Remoh and Mishna Berura (583: 2) “One who sleeps during Rosh Hashana, his luck sleeps too.” refers to the one who sleeps in at the early hours of the day.

Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit”a