Answer based on context:

Owen MacCarthy Reagh   was the 12th Prince of Carbery from 1576 to 1592. He belonged to the MacCarthy Reagh dynasty. Owen was commonly referred to as "Sir" Owen MacCarthy  in the English court records. Owen was the fourth son of Donal MacCarthy Reagh, 9th Prince of Carbery  by his wife Lady Eleanor, daughter of Gerald FitzGerald, 8th Earl of Kildare, Owen became tánaiste in 1567, when his next elder brother Donogh MacCarthy Reagh, 11th Prince of Carbery , father of Florence MacCarthy, succeeded their elder brother Cormac na Haoine MacCarthy Reagh, 10th Prince of Carbery . He was succeeded by the son of his brother Cormac na Haoine, Donal of the Pipes, 13th Prince of Carbery.

When did Owen became tánaiste?
1567