The time duration from AM to AM is generally 12 hours if it refers to 12 AM to 12 PM, but if it means from one AM time to the same AM time the next day (e.g., 8 AM to 8 AM), it is 24 hours. To clarify:

• From one AM time to the same AM time the next day is 24 hours.
• If it is within the same day from AM to PM or PM to AM, the hours vary accordingly but never more than 12 hours in a half-day cycle.

For a specific example:

• From 6 AM to 6 AM the next day is 24 hours.
• From 6 AM to 6 PM (same day) is 12 hours.

Thus, "AM to AM" typically means a 24-hour period if crossing midnight from one day to the next.