"According to Kuiper (1967, 1997: xxiv, quoted with approval by Witzel 1999a: 388), “between the arrival of the Aryans ( . . . ) and the formation of the oldest hymns of the RV a much longer period must have elapsed than normally thought.”"
January 1, 1970
https://en.wikiquote.org/wiki/Franciscus_Bernardus_Jacobus_Kuiper