Henry Wadsworth Longfellow: Quotes about time

The Builders.
Bartlett's Familiar Quotations, 10th ed. (1919)

Hyperion http://www.gutenberg.org/etext/5436, Bk. III, Ch. IV (1839).
Variant: Believe me, every heart has its secret sorrows, which the world knows not, and oftentimes we call a man cold, when he is only sad.
Context: "Ah! this beautiful world!" said Flemming, with a smile. "Indeed, I know not what to think of it. Sometimes it is all gladness and sunshine, and Heaven itself lies not far off. And then it changes suddenly; and is dark and sorrowful, and clouds shut out the sky. In the lives of the saddest of us, there are bright days like this, when we feel as if we could take the great world in our arms and kiss it. Then come the gloomy hours, when the fire will neither burn on our hearths nor in our hearts; and all without and within is dismal, cold, and dark. Believe me, every heart has its secret sorrows, which the world knows not, and oftentimes we call a man cold, when he is only sad."

The Old Clock on the Stairs, st. 9 (1845).
Context: Never here, forever there,
Where all parting, pain, and care,
And death, and time shall disappear,—
Forever there, but never here!
The horologe of Eternity
Sayeth this incessantly,—
"Forever — never!
Never — forever!"

St. 4.
Cf. Andrew Marvell, Upon the Death of Lord Hastings (1649): "Art indeed is long, but life is short".
A Psalm of Life (1839)
Source: Voices of the Night

The Golden Legend http://www.gutenberg.org/files/10490/10490-h/10490-h.htm, Pt. IV, The Cloisters (1872).

Inferno, canto v, line 121.
Bartlett's Familiar Quotations, 10th ed. (1919)

St. 5.
The Day is Done (1845)

The Masque of Pandora and Other Poems (1875)

Hyperion, book iv. Chap. viii.
Bartlett's Familiar Quotations, 10th ed. (1919)

It is not always May, reported in Bartlett's Familiar Quotations, 10th ed. (1919).