The Mishnah in Berachothch2? teaches that one may recite Shema' until the end of the third hour of the day, "for it is the way of the sons of kings to rise by three hours." Why is that the deciding ...
Why do siddurim and Shulchan Oruch OC start with the morning? Since the day starts with night, they should start with Maariv as does the mishnah.