In the Northern Hemisphere, Shavu'ot falls in the late Spring or early Summer. As a result, sunrise is relatively early, so learning "all night" and then praying the morning service at the earliest ...
I have always heard that on the first night of Shavuos you should wait till Tzais HaKochavim for Maariv in order to have Temimos - 7 complete weeks of Sefira. Recently I heard that Harav Ovadia Yosef ...
On Shavous by Night we wait and daven Marriv late in order to have Temmimos,Why dont we daven early on the second night of Pesach for the same reason?