The Kitáb-i-Aqdas - The Most Holy Book
Index term: prayer at dawn, under Sunrise
k33.
O people of Bahá! It is incumbent upon each one of you to engage in some occupation -- such as a craft, a trade or the like. We have exalted your engagement in such work to the rank of worship of the one true God. Reflect, O people, on the grace and blessings of your Lord, and yield Him thanks at eventide and dawn. Waste not your hours in idleness and sloth, but occupy yourselves with what will profit you and others. Thus hath it been decreed in this Tablet from whose horizon hath shone the day-star of wisdom and utterance. The most despised of men in the sight of God are they who sit and beg. Hold ye fast unto the cord of means and place your trust in God, the Provider of all means.
k115.
Blessed is he who, at the hour of dawn, centring his thoughts on God, occupied with His remembrance, and supplicating His forgiveness, directeth his steps to the Mashriqu'l-Adhkár and, entering therein, seateth himself in silence to listen to the verses of God, the Sovereign, the Mighty, the All-Praised. Say: The Mashriqu'l-Adhkár is each and every building which hath been erected in cities and villages for the celebration of My praise. Such is the name by which it hath been designated before the throne of glory, were ye of those who understand.
n142.
the hour of dawn
With reference to attending dawn prayers in the Mashriqu'l-Adhkár, the Bahá'í House of Worship, Bahá'u'lláh has explained that, although the actual time specified in the Book of God is "the hour of dawn", it is acceptable at any time from "the earliest dawn of day, between dawn and sunrise, or even up to two hours after sunrise" (Q&A 15).
q15.
 
Question: Concerning the remembrance of God in the Mashriqu'l-Adhkár "at the hour of dawn".
Answer: Although the words "at the hour of dawn" are used in the Book of God, it is acceptable to God at the earliest dawn of day, between dawn and sunrise, or even up to two hours after sunrise.