This remark appears in the form of a question to add emphasis. Alternate translation: "You know that the day has twelve hours of light!" (See: [[rc://en/ta/man/translate/figs-rquestion]])
People who walk in the light of the day can see well and do not stumble. "Light" is a metaphor for "truth." Jesus is implying that people who live according to truth will be able to successfully do the things that God wants them to do. (See: [[rc://en/ta/man/translate/figs-metaphor]])