1. The last time for the recital of Shema is at the end of the third hour of the day. This means that we divide the day into twelve equal parts (which in the winter are shorter and in the summer are longer), and after the third “hour” is the end of the time for the Shema. Some say we calculate these hours from Netz (Sunrise) and others from Alos (daybreak). (Shulchan Aruch and Mishne Berurah 58)
2. One may not delay the recital of the Shema after this time even to put on Tallis or Tefillin. One must recite the Shema at the right time, and afterwards when he finds a Tallis or Tefillin he should out them om and read the Shema or a chapter of Psalms. He may also not miss the final time for the Shema in order to pray with a quorum. In this case, he should recite it before praying, and then pray with the quorum. (ibid)
