The implied information is that this is when Job would lie down to sleep at night. Alternate translation: "When I lie down to sleep" (See: [[rc://en/ta/man/translate/figs-explicit]])
Job poses this question to emphasize his intense suffering during the hours he should be sleeping. Alternate translation: "I wish I could get up, but night continues." (See: [[rc://en/ta/man/translate/figs-rquestion]])