Regarding the definition of the words "morning", "noon" and "evening", at
which times the currently binding medium Obligatory Prayer is to be
recited, Baha'u'llah has stated that these coincide with "sunrise, noon
and sunset" (Q and A 83). He specifies that the "allowable times for
Obligatory Prayers are from morning till noon, from noon till sunset, and
from sunset till two hours thereafter". Further, 'Abdu'l-Baha has stated
that the morning Obligatory Prayer may be said as early as dawn.
The definition of "noon" as the period "from noon till sunset" applies to
the recitation of the short Obligatory Prayer as well as the medium one.