I don't know if it is his originally, but I first heard that quote from Alan Weiss, who has written over forty books on managing a solo consulting practice.
At the heart of his method is the difference between money and wealth. Money is cash. Wealth is discretionary time. Money is worthless. Wealth is everything.
As long as you're providing your clients and customers with as much value than they need – it doesn't really matter how long it takes you to deliver it. So do everything you can to deliver as quickly as possible. Outsource, sub-contract, only work on the stuff that delivers the greatest results, cut out everything else.
In other words – focus on what really matters. Because you can't make another minute.