When the Psalmist says, “When will you comfort me?” (Ps 118[119]:82), he shows that he is enduring delays, as when he says elsewhere, “And you, Lord, how long?” (Ps 6:4). And this happens either because happiness delayed is sweeter when it does come or because this is how it feels to those who are longing, since what is a short while for the one coming is a long time for someone in love. But the Lord knows when to do what, for he arranges all things by measure and number and weight (Wis 11:21). (EnPs 118[119]/20, 2; PL 37, 1558)

Augustine, of course, thought long and hard about the meaning of time. Chapter XI of his Confessions is devoted to the relation between time and eternity. And one paragraph is famous:

What is time? Who can explain this easily and briefly? Who can comprehend this even in thought so as to articulate the answer in words? Yet what do we speak of, in our familiar everyday conversation, more than of time? We surely know what we mean when we speak of it. We also know what is meant when we hear someone else talking about it. What then is time? Provided that no one asks me, I know. If I want to explain it to an inquirer, I do not know. (Confessions, XI, xiv, 17; Chadwick translation)

Augustine never really answers his question which, in any case, he does not engage philosophically. His focus, instead, is existential and religious. It is time as experienced, as endured, as characterized by how we live that he is interested in. In the quotation above, time is relative to the existential situation of the two people experiencing it.