A day of Lord Brahma in human years.

A one "day-time" period of Lord Brahma is a Kalpa, and one "night-time" period is also a kalpa. 

So there are "2 kalpas" in a 24 hour day of Brahma (see Vaniquotes) 

In human years, "sunrise to sunset" is 4 billion 320 million human years. 

The 1000 Maha-yugas (cycle of 4 yugas) only happen during Brahma's day-time period. 

The night-time period "sunset to sunrise" is the same span of time as above and is when Brahma sleeps while a partial annihilation occurs. There are no Maha-yugas during Brahma's night-time hours. 

One "24 hour day" of Brahma is 8 billion 640 million human years.

A "month of Brahma (30 days)" equals 259 billion 200 million human years.

"12 months of Brahma (360 days)" equals 311 trillion 40 billion human years..*..