Krishna reveals the staggering scale of cosmic time. One day of Brahma lasts a thousand chaturyugas (cycles of the four ages — Satya, Treta, Dvapara, and Kali). His night is equally long. Only those who grasp this immense timescale truly understand what "day" and "night" mean.
Our day is twenty-four hours. Brahma's single day spans billions of years. The mind reels at the comparison. For an ant, a garden is the entire world. For us, what feels like an eternity is just one day in Brahma's life.
This shloka puts everything in perspective. Time is vast beyond imagination, and even Brahmaloka is bound by its passage. True liberation lies beyond time itself — with God.