Lord Brahma lives for 100 of his years which is 311 trillion and 40 billion human years long.

This is also the life span of our material universe that is deep inside the greater surrounding Brahmanda universe that comes from the Body of Maha-Visnu.

In other words, Maha-Visnu creates unlimited massive Brahmanda universes by breathing them out, and then they are absorbed (destroyed) when He again breaths in as seen in painting below.

This means each breath out of Maha-Visnu takes 311 trillion and 40 billion human years, and each breath in takes another 311 trillion, 40 billion human years according to Srimad Bhagavatam.

Presently we are in the 51st year of our Lord Brahma's life time within our material universe.  

Therefore about 156 trillion human years have elapsed since Lord Brahma was born and this material universe began.

As said above, Lord Brahma lives for 100 of his years which is 311 trillion and 40 billion human years, which is also the life span of our Brahmanda material universe and its smaller secondary universe inside it.

Our "secondary material universe" is one of billions and is situated deep inside the greater surrounding massive universe called the Brahmanda universal egg in Srimad Bhagavatam.

There are unlimited Brahmanda universal egg shaped material universes coming from the Body of Maha-Visnu, from His breathing and from the pores of His skin.

After Brahma's death, another 100 of his years (311 trillion, 40 Billion human Years) passes until a new Brahma is born in a new universe and the whole creation begins again. 

This process is repeated again and again in Maha-Visnu's material creation, where deep within each Brahmanda universal shell a secondary universe appears where Garbhodakashayi Visnu, Brahma and the planetary systems are found.

Brahma's day (sunrise to sunset) is divided in one thousand cycles called Maha-yugas. 

Each Maha-yuga has 4 yugas in it-

Satya-yuga is 1,728,000 human years long, 

Treta-yuga is 1,296,000 human years long, 

Dwapara-yuga is 864,000 human years long. 

Kali-yuga is 432,000 human years long (our present yuga) 

There are no Maha-yugas during Brahma's night-time hours from sun-set to sun-rise when Brahma sleeps.

Each Maha-yuga lasts for 4,320,000 years (4 million 320 thousand human years)

Manvantara is Manu's cycle, the one who gives birth and governs the human race. 

Vaivasvata Manu, also referred to as Shraddhadeva and Satyavrata, is the current manu in Brahma's day, the progenitor of the human species. He is the seventh of the 14 manus of the current kalpa (aeon) of Vedic cosmology.

Before and after each manvantara there's a sandhikal as long as krut-yuga and in that time there is all water on earth. 

As explained above, each Maha-yuga consists of four yugas or ages that take 4 million 320 thousand years to pass. 

These yugas get progressively worse from a moral point of view as one proceeds from Satya-yuga (golden age) to Kali-yuga (hypocrisy and quarrel)

As a result, each yuga is of shorter duration than the age that preceded it. 

The current Kali-yuga (the age of hypocrisy and quarrel) began at midnight 17/18 February in 3,102 BC in the proleptic Julian calecalendars. 

As said above, Brahma, the administrator and architect of our "secondary material universe", exists deep inside the Brahmanda universe.

One day-time of Brahma (from sunrise to sunset) is called a Kalpa and is 4 billion 320 million human years long. 

All the 1000 Maha-yugas only appear in Brahma's "day-time hours" and never at night.

One night-time of Brahma (from sunset to sunrise) is also a Kalpa and is 4 billion 320 million in length. 

During the "night-time" period, Brahma sleeps and a partial annihilation takes place, there are no Maha-yugas. 

There are "two Kalpas" in Brahma's 24 hour day which is 8 billion 640 million human years long.

Every Kalpa creates 14 Manus one after the other, who in turn manifest and regulate this world. 

Thus, there are fourteen generations of Manu in each Kalpa. 

Each Manu's life (Manvantara) consists of 71 Maha-yugas (also called Catur-yugas) 

As explained above, each Maha-yuga is composed of four yugas that on occur during Brahma's "day-time" period, 

Satya, 

Treta, 

Dwapara,

Kali. 

And no Maha-yugas exist during Brahma's "night-time" period.

Each morning or the beginning of each day, Brahma creates fourteen additional Manus in sequence just as he has done on the previous 'day.' 

The cycle goes on for 100 of Brahma's years (311 trillion and 40 billion human years) then he perishes (dies)  

A "second" of Brahmā's time equals 98,630 human years long. 

Once Brahma dies there is an equal period of unmanifestation for 311 trillion, 40 billion years, until the next "Brahmanda universe" manifests from the Body of Maha-Visnu.

Then deep within that Brahmanda in a secondary universe, Garbhodakashayi Visnu creates Brahma from His navel who goes on to builds the planetary systems.

The present period we are in is called Kali-yuga, which is within one of the 71 Maha-yugas (set of four yugas) 

Overview of yugas collectivly called a Maha-yuga are-

Satya-yuga (Krita-yuga) = 1,728,000 human years.

Treta-yuga = 1,296,000 human years.

Dwapara-yuga = 864,000 human years.

Kali-yuga = 432,000 human years (as of 2022, 5,124 years have passed; 426,876 years remain). 

Kali-yuga started in 3102 B.C. (over 5000 years ago)..*^*.