Many philosophers have thought about time and our use of it. One of my favorite expression for the urgency to realize what really is important in life is this, by Marcus Aurelius (Roman Emperor and Stoic):
A limit of time is fixed for thee, which if thou dost not use for clearing away the clouds from thy mind, it will go and thou wilt go, and it will never return.
I love the balance this wording strikes between simplicity, symbolism and powerfulness.