The concept of time is very well expounded in Zoroastrian religion. Originally there was Endless Time (zravāneh akaraneh) from which came created time (zravāneh daregho khadhāt).

The ‘Created time’ is further divided into years, months, gahambars, days and gahs, in descending order.  Each period of time is presided by a divine being called ratu. The special ritual and text to invoke the divine beings presiding over time is the Visparad. There are also special prayers for specific time periods, like Gahambars and Gahs.

Timings of the Five Gehs

Each day is divided into five parts called gehs, especially for ritual and prayer purposes. The time periods for these five gehs are as follows:

Hāvan Geh is from sun-rise (whatever the time) to 12:00 noon. In India, since the Indian Standard Time (IST) is taken into consideration and not the local time, the time for Hāvan geh ends at 12:38 pm. The early part of the Hāvan geh is the best time to recite prayers. The Hoshbām can be recited in the first 72 minutes of this Geh. From the beginning of Āvan māh to Vahishtoisht Gatha, Hāvan geh has to be recited even during the time of Rapithwan geh, which is then referred to as the biji (second) Hāvan geh.

Rapithwan Geh is from 12:00 noon to 3:00 pm, or 12:38 pm to 3:38 pm (IST).  From the beginning of Āvan māh to Vahishtoisht Gatha, Rapithwan geh is not recited and instead Hāvan geh is recited, when it is referred to as the biji (second) Hāvan geh.

Uziran Geh is from 3:00 pm or 3:38 pm IST, to sunset (whatever the time).

Aiwisruthrem Geh is from sunset to midnight or 12:38 am (IST). Traditionally the Aiwisruthrem geh started after it was completely dark, and stars started to show in the sky.

Ushahen Geh is from 12:00 midnight or 12:38 am (IST) upto sun-rise (whatever the time). It is not advisable to recite prayers during the first hour of the geh, as at that time, evil forces are most powerful. However, the later part of this geh is the best time for prayers. The last 72 minutes of Ushahen geh is the first part of the Hoshbām period, and the Hoshbām prayer can be recited in this part.

5 Gehs:

Originally in Mazdayasni Zoroastrian religion, the day was divided only in 3 parts, as mentioned in Gatha Ushtavaiti, Yasna 44.5. These were:

1. Usha (from 3.00 am to 12 noon)
2. Arempithwa (from 12:00 non to sunset)
3. Khshapa (from sunset to 3:00 a.m.)

Later on, in the later part of the life of Zarathushtra, a Zoroastrian day was divided into 5 parts,called Gehs. The word Gah or Geh means “time/period of time.” While reciting every prayer, a short invocation to the specific Geh is to be recited in the Fravarāne paragraph. Moreover, in the Khordeh Avesta there are 5 special prayers for each of the 5 Gehs.

While doing the Farazyat prayers, after the Kasti, first the Sarosh Baj is recited and then the prayer dedicated to specific Geh is recited, before doing any other prayers.

Each Geh has its own Yazad which have their co-workers and attendant Yazads/divine beings, as follows:

Geh	Yazads & their co-workers	Associate divine being
Hāvan	Hāvani and Sāvanghi	Meher Yazad
Rapithwan	Rapithwina and Frādat-fshu	Ardibahesht Ameshaspand
Uziran	Uzirina and Frādat-vira	Berez Yazad
Aiwisruthrem	Aiwisruthrema and Frādat-vispa	Asho Farohars (Fravashis)
Ushahen	Ushahina and Berezi	Sarosh Yazad

The larger Geh prayer can be divided into 5 parts.

a. Invocations

b. Introductory extollation (Common)

c. Main matter (particular extollation)

d. Concluding extollation (Common)

e. Final blessing

In each Gah the introductory and concluding extollations are same.

1. Invocations : This introductory part is the invocation or khshnuman. In this part the divine being presiding over the particular Gah and his co-workers are remembered.
2. Introductory Extollation (Common): This second part is common to all Gahs . It starts from the words Ahurem mazdam and ends at ratufritim yazamaide. These two paragraphs are from Yasna 71.2-3. They are in answer to the question “What is the best prayer for the Ratus, that is, divine beings presiding over time. In these paragraphs the following are invoked: Ahura Mazda, prophet Zarathushtra, prophet Zarathushtra’s Fravashi, Amesha Spentas, all Fravashis of material and spiritual worlds, Ratus (divine beings associated with time) and Yazatas who help mankind in times of need.
3. Main matter where the Yazata presiding over the Gah and their co-workers and related issues are remembered, as follows.  

Havan – Khordad, Amardad, Ahurian question, Ahurian creed, Yasna Haptanghaiti

Rapithwin – 5 Gathas, Manthra Spenta, Amesha Spenta

Uzirin – 8 Priestly offices, Luminaries

Aiwisruthrem – Fire, Ritual implements, Zarathushtra, Zarathushtro-tema, Youths, Ladies

Ushahen – Dawn, Light, Heroes, 1^st five Ameshaspands, Mazdayasni religion.

4. Concluding invocation (common): It starts with the words Thwãm ātarem and ends with tāoschā yazamaide. These paragraphs are from Yasna 71.23-24. In these paragraphs are connected occurrences and divine beings right from the beginning till the end of Time. These divine beings help in the bringing of Frashokereti. They are: Fire of Ahura Mazda “supreme divine energy”; Zaothra “divine libations; Barsom “conduit between two worlds”; Apãm Napat “origin of energy” Nairya Sangha and Dãmi upamana “divine messengers”; Iristanam urvāno “the departed souls”; Ratum berezantem “most exalted divine being”, and Vispa sravāo….vareshyamnacha “all past and future words and actions which lead to Frashokereti”.

Gehs and Spirituality:

Zoroastrian scholars like Mr. S. J. Bulsara,  Er. R. R. Motafram and others have showed the inherent spiritual message in the concept of the 5 Gehs. Each of the five gehs indicate the progressive development of the soul.

1. Hāvan: The stage of trials and tribulations for the soul (Hāvani – pounding). The soul has to sustain this stage without succumbing to temptations or being defeated by them. He has to think about benefiting (sāvanghi) the society (visya) despite his hardships.

This is the stage when man has not yet realized divinity. At this stage man has for his guide Mithra, the divine being who presides over friendship, and contracts, and Rãma Khvāstra who gives joy out of the everyday struggle for existence.

2. Rapithwin: The stage where a balance is set. The person is at the mid point (Rapithwina) well poised to realise the upward progress of his soul through the mind. Man starts realizing that he is a soul and his life is given to him as much for the soul as for other things. At this stage he learns to respect all creations and creatures and works for their progress (frādat–fshu).

The divine beings presiding over this stage are Asha Vahishta and Ātar. Man has started understating and realising the order inherent in the Universe. Man realizes that it is through following this order that he will be able to reach the Ultimate Truth. Man starts attaining and absorbing the divine energies. Atar is the Yazad who presides over spiritual fires and the divine energies borne by them.

3. Uziran: The next stage is the spiritual awakening of the soul. The desire of us moi uzareshva expressed in the Gathas, is to reach this stage.  At this stage man has been successful in establishing contact with his Higher Consciousness. He works for the spiritual progress of men (frādat–vira) as he is in complete harmony with fellow human beings.

The  exalted soul now yearns to corroborate with Ahura Mazda and His divine currents (apãm apascha mazda-dhātayāo).

4. Aiwisruthrem: The fourth stage of evolution for the soul is when it is fully developed and is able to communicate and listen to the voices form the other world (aiwi-sru). At this stage man takes on the responsibility of all good living organisms (frādat vispãm hujyāitim).

He becomes a co-worker with the Fravashis who are the guardians of the world. His work is always marked by the courage of conviction (Ama) and crowned with success (verethraghna) of the most supreme kind (vanainiti uparatāt).

5. Ushahen: Dawn of new life for the soul. Time of union of individual consciousness with Universal consciousness. It makes man exalted (berezya). The man who has achieved this stage, has for his guides the divine beings Sarosh (signifying obedience to divine laws. Sarosh is also the Messenger of Vohu Manah), Rashnu (signifying truth at an individual level) and Āshtad (signifying truth at a cosmic level).