“Procrastination is the thief of time.”

1960s, Beyond Vietnam: A Time to Break Silence (1967)
Context: We are now faced with the fact that tomorrow is today. We are confronted with the fierce urgency of now. In this unfolding conundrum of life and history there is such a thing as being too late. Procrastination is still the thief of time. Life often leaves us standing bare, naked, and dejected with a lost opportunity. The tide in the affairs of men does not remain at flood — it ebbs. We may cry out desperately for time to pause in her passage, but time is adamant to every plea and rushes on. Over the bleached bones and jumbled residues of numerous civilizations are written the pathetic words, "Too late."

Variant: Punctuality is the thief of time.

Source: The Gunslinger

Source: Heist Society

Source: Heist Society

Source: The Book Thief

Epigram 43; translation by Robert Allason Furness, from Poems of Callimachus (1931), p. 103
Epigrams

We might know that the work is very urgent and important but we still might find ourselves being slow to start the task.
page 100
Source: Your Job-Hunt Ltd – Advice from an Award-Winning Asian Headhunter (2003), Successful Recruitment in a Week (2012) https://books.google.ae/books?id=p24GkAsgjGEC&printsec=frontcover&dq=nigel+cumberland&hl=en&sa=X&ved=0ahUKEwjF75Xw0IHNAhULLcAKHazACBMQ6AEIGjAA#v=onepage&q=nigel%20cumberland&f=false, Managing Teams in a Week (2013) https://books.google.ae/books?id=qZjO9_ov74EC&printsec=frontcover&dq=nigel+cumberland&hl=en&sa=X&ved=0ahUKEwjF75Xw0IHNAhULLcAKHazACBMQ6AEIIDAB#v=onepage&q=nigel%20cumberland&f=false, Secrets of Success at Work – 50 techniques to excel (2014) https://books.google.ae/books?id=4S7vAgAAQBAJ&printsec=frontcover&dq=nigel+cumberland&hl=en&sa=X&ved=0ahUKEwjF75Xw0IHNAhULLcAKHazACBMQ6AEIJjAC#v=onepage&q=nigel%20cumberland&f=false, p.102

Introductio ad prudentiam: Part II (1727), Gnomologia (1732)