The Shulhan Aruch (Orah Haim 58) mentions the well-known Misva Min Ha’mubhar (special enhancement of a Misva) to recite the Amida right at the moment of sunrise. The most preferred time to recite Shaharit in the morning is such that one begins the Amida right at sunrise.
The question arises as to whether this Misva Min Ha’mubhar relates specifically to the Amida, or also to Shema. One possibility is that the Misva Min Ha’mubhar is to recite the Amida right at sunrise, and thus by necessity, since the Amida must be recited immediately after the Beracha of "Ga’al Yisrael" recited following Shema, one ends up reciting Shema several minutes before sunrise. According to this possibility, the Misva Min Ha’mubhar involves the Amida, and it is only as a practical matter that one who prays Vatikin (reciting the Amida at sunrise) ends up reciting Shema just before sunrise. Alternatively, however, one might say that the value of praying Vatikin involves both the Amida and Shema. The Misva Min Ha’mubhar is to recite the Amida at sunrise, and to recite Shema just before sunrise – not just practically, but intrinsically, because the most preferred time for Shema is just before sunrise.
The Halachic difference between these two perspectives is the question of whether there is value in reciting Shema just before sunrise if one is unable to recite the Amida at sunrise. If one is awake right before sunrise, and he does not have time to recite the full prayer service until later, should he at least recite Shema just before sunrise, as he would if he were praying Vatikin? According to the first understanding, the Misva Min Ha’mubhar of Vatikin relates only to the Amida, and so in this case, there is no value to reciting Shema just before sunrise. But according to the second understanding, Shema should ideally be recited just before sunrise, irrespective of the Amida, and so in this case, it would be preferable to recite the Shema just before sunrise.
Hacham Bension Abba Shaul (Israel, 1924-1998) cites the Rambam (Rav Moshe Maimonides, Spain-Egypt, 1135-1204) as writing that Shema should be recited just before sunrise, and it is only Be’di’abad (after the fact), if one did not recite Shema at that time, that he may recite it later in the morning. The Rambam’s formulation clearly indicates that just before sunrise is the proper time for reciting Shema, independent of the Amida, and thus regardless of whether or not one recites the Amida at sunrise, he should, if he can, recite Shema just before sunrise. This was Hacham Bension’s conclusion, and Hacham David Yosef concurred with this position.
Summary: The preferred time to recite the morning Shema is right before sunrise, even if one is not praying the Amida at sunrise. Therefore, regardless of whether one prays the entire Shaharit service at sunrise, one should try to recite Shema a few minutes before sunrise.
