Lord Caitanya Mahaprabhu and Lord Krsna (as His original Vrindavana Form), come just "once" in a day/night of Lord Brahma.

But only during the "day-time period" to this earth planet, which is "once" every 8 billion 640 million human years.

Lord Caitanya Mahaprabhu and Lord Krsna's appearance in this world is very, very, very rare.

Srila Prabhupada – "Lord Kṛṣṇa and Lord Caitanya appear once in each day of Brahmā." (CC Adi 3.10 Text 10 Purport)

Many take it for granted without realizing how rare Lord Caitanya and Lord Krsna's appearance actually is.

This means Lord Krsna and Lord Caitanya come "once" out of every 1000 maha-yugas. 

All the 1000 maha-yugas occur only in the 12 hour day-time period of Brahma's 24 hour day (during sunrise to sunset)

4 billion 320 million human years equals the 12 hour "day-time period of Brahma" when all the 1000 maha-yugas appear.

At night while Brahma sleeps there are no maha-yugas but instead a partial annihilation of the material universe.

This "night of Brahma" when a partial annihilation occurs, takes another 4 billion 320 million human years. 

So a full 24 hour day of Brahma equals 8 billion 640 million human years.

There are 4 yugas to a maha-yuga all in human years-

1 - Satya-yuga - 1 million 728 thousand years. 

2 - Treta-yuga - 1 million 296 thousand years.

3 - Dvapara-yuga - 864 thousand years.

4 - Kali-yuga - 432 thousand years.

A maha-yuga is also called a catur-yuga and divya-yuga.

Lord Krsna as His original Form appears at the end of just "one" Dvapara-yuga out of every 1000.

And Lord Caitanya appears near the beginning of "one" Kali-yuga with His Sankirtan Movement also out of every 1000 Kali-yugas, just after Krsna's appearance.  

So both Lord Krsna and Lord Caitanya Mahaprabhu appear just "once" during Brahma's 24 hour day-night period, or every 8 billion 640 million human years

So a day-time period from "sun-rise to sun-set" is made up of 1000 maha-yugas and is called a kalpa. 

And a night-time period from "sun-set to sun-rise", where no maha-yugas exist, and a partial annihilation of the material universe occurs while Brahma sleeps, is also called a kalpa.

There are "two kalpas" in a 24 hour day/night of Brahma.

Srila Prabhupada –"At the end of the Dvāpara-yuga of the twenty-eighth divya-yuga (Maha-yuga), Lord Kṛṣṇa appears on earth with the full paraphernalia of His eternal Vraja-dhāma." (CC Adi 3.10 Text 10)

Srila Prabhupada – "Now is the term of Vaivasvata Manu, during which Lord Caitanya appears. First Lord Kṛṣṇa appears at the close of the Dvāpara-yuga of the twenty-eighth divya-yuga (maha-yuga), and then Lord Caitanya appears in the Kali-yuga of the same maha-yuga. 

Lord Kṛṣṇa and Lord Caitanya appear "once" in each day of Brahmā, or once in fourteen manv-antaras, each of seventy-one divya-yugas (maha-yugas) in duration. 

From the beginning of Brahmā’s day-time period of 4 billion, 320 million human years, six Manus appear and disappear before Lord Kṛṣṇa appears. 

Thus 1 billion, 975 million  320 thousand years of the day of Brahmā elapse before the appearance of Lord Kṛṣṇa. This is an astronomical calculation according to solar years." (CC Adi 3.10 Text 10)

Devotee - "Śrīla Prabhupāda, does Lord Caitanya Mahāprabhu also appear every day of Brahma?"

Srila Prabhupāda - "Yes, following Kṛṣṇa. Kṛṣṇa comes in the Dvāpara-yuga. There are four periods of each yuga: Satva, Tretā, Dvāpara, Kali. So Kṛṣṇa comes at the end of Dvāpara-yuga, and Caitanya Mahāprabhu comes in the Kali-yuga." (Lecture, SB Canto 6 Ch 1 Text 3 Melb, May 22, 1975)

So as explained above, there are no maha-yugas in Brahma's 12 hour "night-time" period (that also takes 4 billion 320 million human years to pass) while Brahma sleeps and a partial annihilation takes place.**.

From Matchless Wondergifts.