"Youth is wasted on the young" is kind of about time...
"Time is money" is another.
I like "Today is the day to plan for tomorrow."
David Norris
How you spend your time is more important than how you spend your money. Money mistakes can be corrected, but time is gone forever. .
And for more elegant ones:
"Clocks slay time... time is dead as long as it is being clicked off by little wheels; only when the clock stops does time come to life." by William Faulkner is pretty.
"As if you could kill time without injuring eternity." by Henry David Thoreau
"Men talk of killing time, while time quietly kills them." ~Dion Boucicault
"But what minutes! Count them by sensation, and not by calendars, and each moment is a day." ~Benjamin Disraeli
Time wastes our bodies and our wits, but we waste time, so we are quits.