To answer "how long until PM," assuming the question is about how long until the start of PM (which begins at 12:00 noon or 12:00 PM):

• The 12-hour clock divides the day into AM (midnight to just before noon) and PM (noon to just before midnight).
• PM begins at 12:00 noon (12:00 PM) each day.
• The duration from the current time to the next PM start will depend on the current time of day.
• For example, if it is currently 11:00 AM, there is 1 hour until 12:00 PM (the start of PM).
• If it is already past noon, the next PM period would start at noon the next day, roughly 24 hours minus the current time from midnight.

More specific calculation requires knowledge of the current time in your time zone. Generally, the time until PM is the time until 12:00 noon today if it is before noon or the time until noon the next day if it is after noon. In summary: PM time begins exactly at 12:00 noon (12:00 PM). The duration until PM starts depends on the current time, counting down to the next 12:00 PM mark on the clock.