Fasting

Holy Days

Establishment:
In the sacred Laws of God, in every cycle and dispensation, there are blessed feasts, holidays and workless days. On such days all kinds of occupations, commerce, industry, agriculture etc., are not allowed. Every work is unlawful. All must enjoy a good time, gather together, hold general meetings, become as one assembly, so that the national oneness, unity and harmony may become personified in all eyes. As it is a blessed day it should not be neglected or without results by making it a day limited to the fruits of mere pleasure. During such blessed days institutions should be founded that may be of permanent benefit and value to the people so that in current conversation and in history it may become widely known that such a good work was inaugurated on such a feast day.
    (`Abdu'l-Baha: Lights of Guidance, p. 303)

All Feasts have attained their consummation in
          the two Most Great Festivals, and in the two other
          Festivals that fall on the twin days # 110
     This passage establishes four great festivals of the Baha'i year. The two designated by Baha'u'llah as "the two Most Great Festivals" are, first, the Festival of Ridvan, which commemorates Baha'u'llah's Declaration of His Prophetic Mission in the Garden of Ridvan in Baghdad during twelve days in April/May 1863 and is referred to by Him as "the King of Festivals" and, second, the Bab's Declaration, which occurred in May 1844 in Shiraz. The first, ninth and twelfth days of the Festival of Ridvan are Holy Days (Q and A 1), as is the day of the Declaration of the Bab.
     The "two other Festivals" are the anniversaries of the births of Baha'u'llah and the Bab. In the Muslim lunar calendar these fall on consecutive days, the birth of Baha'u'llah on the second day of the month of Muharram 1233 A.H. (12 November 1817), and the birth of the Bab on the first day of the same month 1235 A.H. (20 October 1819), respectively.
    (The Universal House of Justice: Aqdas: Notes, pp. 224-225)

In the Baha'i calendar the first month of the year and the first day of each month are given the name "Baha". The day of Baha of the month of Baha is thus the Baha'i New Year, Naw-Ruz, which was ordained by the Bab as a festival and is here confirmed by Baha'u'llah ...
    (The Universal House of Justice: Aqdas: Notes, p. 225)

In addition to the seven Holy Days ordained in these passages of the Kitab-i-Aqdas, the anniversary of the Martyrdom of the Bab was also commemorated as a Holy Day in the lifetime of Baha'u'llah and, as a corollary to this, Abdu'l-Baha added the observance of the Ascension of Baha'u'llah, making nine Holy Days in all. Two other anniversaries which are observed, but on which work is not suspended, are the Day of the Covenant and the anniversary of the Passing of Abdu'l-Baha.
    (The Universal House of Justice: Aqdas: Notes, p. 225)

Observance:
With reference to your question in connection with the observance of Baha'i Holy Days; the Baha'i day begins and ends at sunset. The night preceding a Holy day is therefore included in the day, and consequently work during that period is forbidden.
    (Shoghi Effendi: Dawn of a New Day, p. 68)

He [Shoghi Effendi] thinks it is better for Baha'i doctors not to work on our 9 Holy Days - but, of course, that does not mean they should not attend to very sick people and emergencies on these days.
    (Shoghi Effendi: Lights of Guidance, p. 288)

The beloved Guardian made it absolutely clear that the command to cease work during the nine Holy Days is a matter for conscientious obedience by every individual believer.
    (The Universal House of Justice: Lights of Guidance, p. 301)

The exchanging of presents among believers or the giving of gifts to children is not an integral part of any of our nine Baha'i Holy Days. There is no prohibition against it, and it is, as you say, a custom among Persian believers such as the Baha'i to whom you spoke, to exchange gifts at Naw-Ruz.
    (The Universal House of Justice: Lights of Guidance, p. 302)