Bg 8.23

yatra kale tv anavrttim
avrttim caiva yoginah
prayata yanti tam kalam
vaksyami bharatarsabha

Word for word: 
yatra — at which; kale — time; tu — and; anavrttim — no return; avrttim — return; ca — also; eva — certainly; yoginah — different kinds of mystics; prayatah — having departed; yanti — attain; tam — that; kalam — time; vaksyami — I shall describe; bharata-rsabha — O best of the Bharatas.

Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
O best of the Bharatas, I shall now explain to you the different times at which, passing away from this world, the yogi does or does not come back.

Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
The unalloyed devotees of the Supreme Lord, who are totally surrendered souls, do not care when they leave their bodies or by what method. They leave everything in Krishna’s hands and so easily and happily return to Godhead. But those who are not unalloyed devotees and who depend instead on such methods of spiritual realization as karma-yoga, jñana-yoga and hatha-yoga must leave the body at a suitable time in order to be sure of whether or not they will return to the world of birth and death.

If the yogi is perfect he can select the time and situation for leaving this material world. But if he is not so expert his success depends on his accidentally passing away at a certain suitable time. The suitable times at which one passes away and does not come back are explained by the Lord in the next verse. According to Acarya Baladeva Vidyabhusana, the Sanskrit word kala used herein refers to the presiding deity of time.