Thinking of the ever-decreasing amount of (earthly) life left can be depressing. That's the A-theoretic way. But there is a B-theoretic way: one can think of the span of one's life as a puzzle or painting that one needs to fill in in good ways. At any time t during one's life, one is only obligated to fill in the remaining parts of the puzzle or painting, the parts that are causally dependent on the here-and-now.
There is, in a sense, less stress the less of the puzzle or painting remains, since there is less of a future to make decisions for. Of course, one might have screwed up in the past, and now one has less time to compensate. But, apart from cases of genuine moral dilemmas, one is not obliged to do more than the best one can now do, and God's forgiveness is always available. The A-theorist can say many of the same things, but to me, these things fit better with the B-theory.
Take an extreme case. Suppose one is down to one minute left. Well, then, the problem is merely how best to live that minute. In a way, that is momentous, since it is a culminating minute. But, then again, it's only a minute, and unless one has a likelihood of deep wisdom, or sins that one hasn't repented of, the problem is not so great: the problem is merely how to live one minute.
At the same time, thinking of life in this way, as a puzzle or a painting to fill in, makes each moment crucial. For while a painter can always paint over a portion, we paint our lives in a way that does not allow for that. This is a way in which eternalist theories of time may lead to a cherishing of each moment, of living it out as best one can, since that moment always stands. A presentist can say similar things, but they seem less compelling then, I think.
The above is not an unattractive picture of life. Notice that there are two views here: one of life as a puzzle and the other as a painting. I think there is a way in which both views are right. Life is like a painting, but we are not the primary painter. The primary painter is God. For us, it is more like a puzzle, in that we should be trying to paint it in not according to our conception of what life is artistic, but according to God's. Moreover, we need not navel-gaze and puzzle-solve all that much, but all we need to do is love, and then God will take care of the painting (think of the life of a St Francis—here, there is a painting, but St Francis surely didn't care nearly as much about the painting, i.e., about his life, as about God, neighbor and the rest of creation). So there is a way in which the analogy isn't so good at all.