In Meditations, Marcus Aurelius addresses the issue of procrastination:
Attend to the matter which is before thee, whether it is an opinion or an act or a word. Thou sufferest this justly: for thou choosest rather to become good tomorrow than to be good today.
I think it is just as important to keep in mind that your 'tomorrow' may not come at all, and maybe all you ever have is your 'now'.