The essence of Muhurta is the time which expands to 2 Ghatis. It is actually 48 minutes. You want to perform a specific activity and you are looking for a perfect time so that you can get the desired results. The placement of the Sun and Moon are very important in fixing a Muhurta. A Muhurta is fixed on the basis of a lot of parameters like Ayana, Month, Nakshatra, Tithi, Vaar, Nakshatra, Yoga, and Karana.
‘Muhu’ means ‘moment’ and ‘rta’ means ‘order’. This concept is created based on the ideas given in RigVeda about the Speed of Light. There are 30 muhurtas in a Nakshatra Ahoratra (sidereal day and night reckoned from one sunrise to the next sunrise). The time from Sun rise to local noon time is divided into 7½ Muhurta. Likewise, local noon to Sun set, Sun set time to Midnight, midnight time to sun rise time is also divided by 7½. This time will come into 30 when 7½ x 4= 30.
The 4 conjunct points sunrise, local noon, sunset and midnight are called Gayatri Padha. The time span between the 4points are 7½ wide, so these 4 points make a day. And it is called Prahara. The last ½ muhurta in the morning and the first ½ muhurta in the after noon is called as Abhijit Muhurta. This muhurta is known to be very auspicious and it can be used only in an urgency.
The exact time of Abhijit Muhurta depends upon the length of the day and the time of Sunrise. Both varies every day.