The minimum duration of a journey which exempts the
believer from fasting is defined by Bahá’u’lláh (Q and A 22 and
75). The details of this provision are summarized in the
Synopsis and Codification, section IV.B.5.a.i.-v.
Shoghi Effendi has clarified that while travellers are
exempt from fasting, they are free to fast if they so wish. He
also indicated that the exemption applies during the whole
period of one’s travel, not just the hours one is in a train or
car, etc.