Facing a DO NOT ENTER sign at the mouth of a street, you wonder whether the restriction might only apply at certain times of day, the way some turn restrictions do. Can a DO NOT ENTER sign be time-limited?

Correct answer: D. No — a DO NOT ENTER sign always applies; time-restricted entry is signed with a different sign that shows the times

No. Book 5 is explicit: the DO NOT ENTER sign "must be used for absolute conditions with no time restrictions. If there are certain time periods for which the sign does not apply, then the condition is no longer absolute, and the special meaning of the sign is compromised." Where entry is restricted only during certain hours, a different sign is used — one of the turn control signs with an "A" suffix that carries the times on its face, such as Rb-10A, Rb-11A or Rb-12A. So a plain DO NOT ENTER sign always means now, whatever the hour: there is no clock behind it to check.

Source: MTO Driver's Handbook: Ontario Traffic Manual, Book 5 — Regulatory Signs (December 2021), Section 9 — DO NOT ENTER Sign (Rb-19)