In Claris Organizer, it is possible to change the time values in an appointment by using the plus (+) and minus (-) keys. You may use the plus key to increase the time and the minus key to decrease the time of an appointment. If these keys do not work properly for you, check the format of the time in your Date and Time control panel. If the suffix for AM or PM has been changed to only show an "A" or a "P," Claris Organizer will not go past 12:00 (noon) and will loop around to 1:00 A.
The workaround is to enter the time manually, or to change the time format to show "AM " or "PM" rather than "A" or "P" respectively.
The Date & Time Control Panel may also be set to military time.