The Kitáb-i-Aqdas
Questions and Answers
83Question: Concerning the definition of “morning,” “noon” and “evening”.
Answer: These are sunrise, noon and sunset. The allowable times for Obligatory Prayers are from morning till noon, from noon till sunset, and from sunset till two hours thereafter. Authority is in the hand of God, the Bearer of the Two Names.
Authority of God,   K161, K162, K163
Times for Obligatory Prayer,   K6, 144, n5