**Muhoort
This word is more used to indicate a certain time period. People use at as. "Hurry, hurry, Muhoort is passing away" because a certain time period is passing away - it is about only 1/2 an hour long

#Ayan
There are two Ayan - Uttaraayan and Dakshinaayan. In Uttaraayan the Sun's direction is towards North (from June to December) and in Dakshinaayan its direction is towards South (from December to June).

Thus Bhagvaan Soorya, Swaamee of all planets, constellations, and stars revolve in 12 Rashi (Signs), from Paramaanu to Samvatsar time. According to Soorya, Brihaspati, Savan, Chandramaa and Nakshatra, this time period is called Samvatsar (according to Soorya), Parivatsar (according to Brihaspati), Idaavatsar (according to Savan), Anuvatsar (according to Chandramaa) and Vatsar (according to Nakshatra). Thus this Soorya is the cause of creating five types of years.

Yug = There are 4 Yug, Sat, Tretaa, Dwaapar, and Kali. They are in the proportion of 4:3:2:1 thousands Divine-years. Thus :
  Sat ......... 4,000 Divine-years + 800 years of Sandhyaa and Sandhyaansh)
  Tretaa ..... 3,000 Divine-years + 600 years of Sandhyaa and Sandhyaansh)
  Dwaapar ... 2,000 Divine-years + 400 years of Sandhyaa and Sandhyaansh)
  Kali ......... 1,000 Divine-years + 200 years of Sandhyaa and Sandhyaansh)

In whatever Yug whatever thousand years are, its double the years in hundreds are in its Sandhyaa and Sandhyaansh, such as Kali Yug has 1,000 divine years so its double means 2, and in hundreds i.e. 200 years should be the Sandhyaa and Sandhyaansh. The beginning of Yug is Sandhyaa and the end of the Yug is Sandhyaansh. So their duration is in hundred years and in between them is the Yug. Thus their total time period is:

  Sat ......... 4,800 Divine-years x 360* = 1,728,000 Human-years
  Tretaa ....  3,600 Divine-years x 360  =  1,296,000 Human-years
  Dwaapar ... 2,400 Divine-years x 360  =    864,000 Human-years
  Kali ......... 1,200 Divine-years x 360  =    432,000 Human-years
  Total   =   12,000 Divine-years x 360  =  4,320,000 Human-years

 *because        1 Human-year        = 1 Divine-day
                      360 Divine-days    = 1 Divine-year 
    therefore     360 Human-years    = 1 Divine-year
therefore  4,320,000 Human-years x 1,000 4-Yug period
                    = 4,320,000,000 years = Brahmaa's day and
                    = 4,320,000,000 years = Brahmaa's night

Thus  8,640,000,000 Human-years  =  Brahmaa's one day and night
Thus  8,640,000,000 x 360 days (Brahmaa's days) = Brahmaa's one year
And Brahmaa's age = 100 Divine-years 

So Brahmaa's age = 8,640,000,000 Human-years x 360 days (Brahmaa's day+nights) x 100 years

Beyond Tri-Lok, from Mahar Lok, to Tapah Lok, to Brahm Lok 1,000 Human 4-Yug period is one day and the same period of time, 1,000 Human 4-Yug, is one night in which Brahmaa Jee sleeps. When Brahmaa Jee night ends, then our Kalp starts on Prithvi, and it ends when Brahmaa Jee's day ends. 

This is Brahmaa Jee's day only and He has His night also of the same length. In the day time He is awake and creates the Universe. In the night time He sleeps and it is the time of Pralay. At that time it is all dark and water everywhere, no creation, no light except of Rishi's light, and everything is in sleep state. Brahmaa Jee with the help of Tamo Gun stops His Creation, stays calm and the whole Universe enters in His body.

When Brahmaa Jee's night ends our Kalp starts on this Prithvi. In one Kalp there are 14 Manu - Swaamee of Manvantar. Because one Kalp is of 1,000 Human 4-Yug period, thus one Manu rules for 71 9/16 Human 4-Yug period.

71+9/16 Human 4-yug period  = 1 Manvantar (present Manvantar is the 7th)
1,000 Human 4-Yug period      = 14 Manu Period
1,000 Human 4-Yug period      = Brahmaa's day
1,000 Human 4-Yug period      = Brahmaa's night
2,000 Human 4-Yug period      = Brahmaa's one day+night
                      360 days      = 1 Divine year of Brahmaa Jee
            100 Divine years       = Brahmaa Jee's age

So Brahmaa Jee's age = 100 Divine years x 360 days x 2,000 Human 4-Yug
                                = 36,000 Divine days X 2,000 Human 4-Yug 
                                = 36,000 Divine days X 

50 Divine Years           = 1 Paraardh (presently 2nd Paraardh is going on)
                                   Brahmaa Jee's half age
1,000 4-Yug period      = 1 Kalp

And this 1,000 4-Yug period or 1 Kalp is Brahmaa Jee's age. These 100 Divine Years also pass quickly.

Now this 2 Paraardh time or Brahmaa's 100 Divine years is Bhagvaan's one Nimesh. This Nimesh, from Paramaanu to two Paraardh is all powerful, but still does not control Shree Hari. It rules only Jeev with physical body.