1) It is a good custom not to sleep during the day of Rosh Hashanah, as the Yerushalmi writes that one who sleeps on Rosh Hashanah’s horoscope is also sleeping. The Ar”I Zal said the after midday one can sleep. (Shulchan Aruch and Mishne Berurah 583)
2) However, the idea of not sleeping is only when in place of sleeping one learns or recites Psalms. One who wastes the time is considered like having slept. (ibid)
