About how long ago did the Bantu migration occur?

The Bantu migration occurred over a long period of time generally considered to have run from about 3000 years ago until 500 years ago.

There is some minor debate but generally speaking linguistic analysis indicates that tribes of speakers of the Bantu languages began migration south and east (from the present area of the Congo or Nigeria) as early as 2000 BCE with periodic migrations continuing as recently as 1500-1700 CE