The period following sunset with which the Jewish day began (Genesis 1:5; Mark 13:35). The Hebrews reckoned two evenings of each day, as appears from Exodus 16:12: 30:8; 12:6 (marg.); Leviticus 23:5 (marg. RSV, "between the two evenings"). The "first evening" was that period when the sun was verging towards setting, and the "second evening" the moment of actual sunset. The word "evenings" in Jeremiah 5:6 should be "deserts" (marg. RSV).
These dictionary topics are from M.G. Easton M.A., D.D., Illustrated Bible Dictionary, Third Edition, published by Thomas Nelson, 1897. Public Domain, copy freely.
Easton, Matthew George. "Entry for 'Evening'". "Easton's Bible Dictionary".