http://revach.net/article.php?id=4746

Section: Halacha   Category: Tshuvos
Rav Shlomo Zalman Auerbach - Sleeping On Rosh HaShanah & Davening Vasikin
The gemara Yerushalmi says that if someone sleeps on Rosh HaShanah, his Mazal will sleep all year.  The Rema brings this as well (OC 583:2).  The Mishna Brura (SK 9) writes that the main problem is before Chatzos but not after.  If so should you wake up by Alos HaShachar on Rosh HaShanah morning, and not sleep once the day begins?

Although the Mateh Ephraim (584:1) and others hold that you should wake up before dawn, Rav Shlomo Zalman Auerbach (Halichos Shlomo 2:1:23) says that this is not necessary with regard to this halacha.  The reason is that in previous generations people woke up early, and sleeping past Alos on Rosh Hashanah was a lazy things to do.  Today people sleep past dawn and the sleep is considered part of the night sleep.  Nowadays this halacha only applies to going to sleep during the day after you already were up.

With regard to the Minhag of people davening with the Netz on Rosh HaShanah, Rav Shlomo Zalman says that this has nothing to do with not sleeping.  Rather, Netz is the best time to daven, and on a critical day like Rosh HaShanah where we need our Tefilos to be Niskabel, many people choose to daven at the most auspicious hour, which is Netz.

Important Note: We bring this tshuvah as a starting point for discussion and not to convey any halacha.  We try to convey the Tshuva to the best of our ability. We admit that our understanding may not be accurate. One should learn the tshuva to verify the accuracy of our interpretation.  Please understand that this Tshuva may not be the final word on this topic. One should consult a Rav before drawing any conclusions.