The minimum duration of a journey which exempts the believer from fasting
is defined by Baha'u'llah (Q and A 22 and 75). The details of this
provision are summarized in the Synopsis and Codification, section
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.