Jesus the Christ - James E. Talmage

 Talmage wrote of the crucifixion -

"At the ninth hour, or about three in the afternoon, a loud voice, surpassing the most anguished cry of physical suffering issued from the central cross, rending the dreadful darkness. It was the voice of the Christ: “Eloi, Eloi, lama sabachthani? which is, being interpreted, My God, my God, why hast thou forsaken me?” What mind of man can fathom the significance of that awful cry? It seems, that in addition to the fearful suffering incident to crucifixion, the agony of Gethsemane had recurred, intensified beyond human power to endure. In that bitterest hour the dying Christ was alone, alone in most terrible reality. That the supreme sacrifice of the Son might be consummated in all its fulness, the Father seems to have withdrawn the support of His immediate Presence, leaving to the Savior of men the glory of complete victory over the forces of sin and death..."

Talmage, James E.. Jesus the Christ with Live Index (p. 282). Deseret Book Company. Kindle Edition. 

In my mind, the agony of the Savior on the cross may have been as long as that in Gethsemane.