Danna (Sumerian) or Beru (Akkadian) is a word denoting a unit of time consisting of two hours.
[1] There were twelve Danna in a day.
[2] In Hellenistic times the Danna was halved with the introduction of the temporal hours and the number of daylight hours increased from twelve to twenty-four.
The conversion was based on the ancient Egyptian precursors of the 24 seasonally - equal hours.
A 24-hour division of the day could not be proven in inscriptions on Babylonian tablets, which is why the Babylonians cannot be used as the originators of the 24-hour division of the day.