1. One who did not read the Shema at the right time, may also read it afterwards. However, he does not receive the merit of fulfilling the commandment to read the Shema. Rather, he receives reward like one who reads the Torah. It is nevertheless good to read it, even later on in the day, in order to accept the yoke of the kingship of heaven upon himself. (Shulchan Aruch and Mishne Berurah 58)
2. The third paragraph of the Shema, which contains the mentioning of the exodus from Egypt, is an obligation to be read even after the allotted time for the rest of the Shema, as there is no fixed time for the mentioning of the Exodus from Egypt. It is an obligation all day. (ibid)
