Letters 22.6

But he also adds that one should attempt nothing except at the time when it can be attempted suitably and seasonably. Then, when the long-sought occasion comes, let him be up and doing. Epicurus forbids us to doze when we are meditating escape; he bids us hope for a safe release from even the hardest trials, provided that we are not in too great a hurry before the time, nor too dilatory when the time arrives.

Seneca, Letters to Lucilius 22.6, translated by Richard Mott Gummere