ובבקר אמר למלך
“In the morning speak to the King.” (Esther 5:14)
What was the rush, why did Haman have to speak to the king in the morning?
Rav Yonasan Eibshitz (Yaares Devash, Vol. 1, Derush 17) explains: The Gemara in Berachos (9b) says that the “vasikin” - “devoted ones” - who were meticulous in performing mitzvos, would rise early in the morning to complete the recitation of Shema before sunrise and then say the Shemoneh Esrei at sunrise so that they could be: סומך גאולה לתפילה –“recite the blessing about redemption (which follows immediately after Shema) together with Shemoneh Esrei”. Rabbi Yose ben Elyakim testified: “If one joins the blessing about redemption with Shemoneh Esrei at sunrise, no harm will befall him all that day.”
Hence, to be sure that the hanging of Mordechai would be approved by the King, they told Haman to discuss it with the King early in the morning before Mordechai recited Shema and the Shemoneh Esrei.
Perhaps with this we can understand the widespread minhag to daven with sunrise on Purim. We see from the Megillah the importance of davening with sunrise, therefore, on a day where a large focus of the day is about Megillah, it only makes sense to daven then.
