When chanted the maha-mantra is a petition to God - “O Krishna, O energy of Krishna, please engage me in Your service.”

Harinama harinama harinama eva kevalam 

kalau nastyeva nastyeva nastyeva gatir anyatha

‘'In this Age of Kali there is no other means, no other means, no other means for self-realization than chanting the holy name, chanting the holy name, chanting the holy name of Lord Hari.’'

Maha means “great” and mantra means “sacred chant for deliverance.”

Hare Krishna, Hare Krishna

Krishna Krishna, Hare Hare

Hare Rama, Hare Rama

Rama Rama, Hare Hare.

When chanted the maha-mantra is a petition to God -

“O Krishna, O energy of Krishna, please engage me in Your service.”

Lord Caitanya Mahaprabhu only comes "once" out of every 1000 Maha-yugas, that ONLY happen in the "day-time" hours of Brahma's 24 hour day.

So again, there are no yuga's during Brahma's night-time hours.

Just to be clear again, the 1000 Maha-yugas happen in Brahma's day-time between "Sunrise and Sunset". 

Each Maha-yuga is made up of four yugas, Satya, Treta, Dvarpara and Kali, we are presently in the last yuga,  Kali-yuga that lasts for 432,000 human years.

There are 4 billion 320 million human years in Brahma's day-time hours and 4 billion 320 million human years in Brahma's night-time hours.

This Kali-yuga is very special because Lord Caitanya has come to it in 1486 AD in West Bengal India.*