The Pulpit Commentary on Genesis 16:3

And Sarai Abram's wife took Hagar her maid the Egyptian, after Abram had dwelt ton years in the land of Canaan (i.e. in his eighty-fifth, and her seventy-fifth year; a note of time introduced, probably, to account for their impatience in waiting for the promised seed), and gave her to her husband Abram to be his wife.