“At what time does one begin to recite the Shema in the morning?…Rabbi Eliezer says,
‘[When one can distinguish] between blue and green, and concludes it by sunrise…” 
“…Rabbi Berona… joined g’ulah with t’filah, and a smile didn’t leave his face all day.” 
Rabbi Berona followed the custom of the Vatikin or ותיקים who, completing the Shema and the G’ulah exactly at sunrise (as per Rabbi Eliezer), could then recite the T’filah without pausing. Declaring G-d’s absolute Dominion (i.e. the Shema) and irresistible redemptive power (i.e. the G’ulah), they could then place their lives in G-d’s hands (i.e. the T’filah) in an unbroken contemplative stream. Their stringency regarding timing enhanced their kavannah and devotion.
“A smile didn’t leave his face”: His overflowing happiness was visible to all.
He loved G-d, and believed he was doing what G-d best wanted him to do. His joy, then, was not in his own will, but in G-d’s. Not in himself, but in G-d. Not in his self, but in G-d’s Self. Rejoicing in G-d, he felt G-d’s realness and closeness. Harmonizing himself with that Realness by love of and obedience to G-d through following Rabbi Eliezer’s opinion in the mishnah (thereby surrendering his own will/self), his attention turned from himself to G-d; he transcended. Transcending, he ceased to know anything other than Divine Bliss. Knowing only Divine Bliss, he radiated joy all day.
His joy was not in his saying particular words at a particular time; not in his own accomplishment. His joy was not “his” at all. His joy was the joy and love of G-d’s Presence, radiating out as his own life. G-d’s Joy and Love were his own Self.
We experience the same joy, even for a moment, in any sincere prayer.
“The focus of prayer is not the self. A man may spend hours meditating about himself, or be stirred by the deepest sympathy for his fellow man, and no prayer will come to pass. Prayer comes to pass in a complete turning of the heart toward G-d, toward His goodness and power. It is the momentary disregard of our personal concerns, the absence of self-centered thoughts, which constitute the art of prayer. Feeling becomes prayer in the moment in which we forget ourselves and become aware of G-d. When we analyze the consciousness of a supplicant, we discover that it is not concentrated upon his own interests, but on something beyond the self. The thought of personal need is absent, and the thought of divine grace alone is present in his mind. Thus, in beseeching Him for bread there is one instant, at least, in which our mind is directed neither to our hunger nor to food, but to His mercy. This instant is prayer.” 
The “secret” of the Vatikin, then – the essence of their prayer – isn’t simply a stringency regarding at what time they prayed; if it were, everyone who prayed at the same time would have the same experience. Rather, as Rabbi Heschel tells us, it’s how much more of their attention they gave to G-d rather than to themselves – especially, but not exclusively, while praying. Their strin-gency was an expression of their eagerness to recognize and proclaim G-d’s Presence, and to give it absolute primacy in their daily lives. They cared enough for G-d, and for living a life filled with the awareness of G-d, to want to declare G-d’s Kingship immediately as each day began. If we pray at dawn, thinking that timing itself is the critical element, we’re imitating the outward form of Vatikin piety, without necessarily being enlivened by the same inner devotion as theirs.
Ultimately, the halachah is that one may recite the Shema until 10 AM. Rabbi Eliezer’s opinion is considered a praiseworthy option, but not a requirement.
“…One may do much or one may do little; it is all one, provided he directs his heart to Heaven [i.e. to G-d].” 
We can say as much, ourselves. It’s the heart that G-d wants. Let us give G-d our enthusiasm.