Rahu is the severed head of the demon called Svarbhanu who is responsible for swallowing the Sun causing eclipses. As per Hindu tradition, Rahu Kaal covers 90 minutes every day between Sunrise and Sunset. Rahu Kalam refers to the inauspicious time in a day to start any new activity. 

In iconography, Rahu is depicted with a human head and serpent body and seated in a chariot, drawn by eight black horses. The other name of Rahu is Bhayanaka. Considered one of the nine planets in Astrology, Rahu is considered malefic. 

While one day of the week is dedicated to seven other planets, about 90 minutes every day, is dedicated to Rahu which is considered Rahu Kalam. 

Rahu is said to cover and encircle the mind during Rahukalam, just as it overshadows the planets, making the mind blank. As a result, mental clarity suffers, and all the crucial tasks run the risk of being ruined. Rahu Kalam is hence viewed as unlucky.

During Rahu Kalam new ventures, projects or jobs should not be started. Travel for work-related must be avoided. One must also refrain from executing any auspicious rituals, like Mundan, Upanayanam, House warming, marriage, and engagement.

In the same way, no transactions, buying or selling of products, jewelry, or other items must take place during this time. One must also not perform yajna or Homa or Pooja during this period. 

Yamagandam:

Yamagandam is the time of the day when Ketu rules for one and a half hours at various times during the week. The ruling period of Kethu or Yamagandam timings changes every day, based on the weekday. The Yamagandam time is also dependent on the time of sunrise and sunset.

Yamagandam means death time. Only death ceremonies are performed during Yamagandam. Any activity commenced during this time invites the ‘death’ of the work or energies relating to that work. Activities during Yamagandam lead to failure or destruction of the result. Avoid commencing important, money-related, or travel activities, during this time. Leave your current location have your meeting, or start your activity earlier than or after the Yamagandam time. Don’t be tempted to use this time slot to end some issues as it is dangerous to plan an activity during this time as the result could be a failure for you.

Yama Gandam as the name suggests is the period associated with the Hindu demi-god ‘Yama’, who is considered as lord of death.

In India, there is a practice of checking auspicious times for performing any new initiative related to official and personal work. While checking for a good time based on panchang (panchangam in Tamil) and Hora concepts of Vedic astrology, people usually avoid the time of Yama Gandam.

  This Yama Gandam period varies based on the sunrise and sunset timings.

  After the daylight, hours are divided into 8 sections. 

Avoid commencing important, money-related, or travel activities, during this time.

Rahu Kalam:

10.30 am to 12.00 am

Yamagandam:

3.00 pm to 4.30 pm

 

Read more : https://www.astroved.com/astropedia/en/friday-rahukalam-and-yamagandam-timings