I apologize for not being clear on the parameters. I run on Mt Lion 10.8.2 on my Mac and iOS 6.1.2 on my iPhone 4S. I make the entries on the Mac using the latest version of iCal. I run Calendar on the iPhone and sync via iTunes (now on the latest version downloaded yesterday). I do not use the Cloud for anything. All syncing is between the iPhone and the Mac.
This problem has been present for a few months. I can't remember when it began. I've wondered if iCal has been corrupted, but downloading and reinstalling Mt. Lion might not do any good if the corruption is in the data. On the other hand, it might do the job. The alarm that goes off in the night when it has reset to 15 hours is the iPhone alarm, but I never have the 15 hour experience without its also showing up on iCal on the Mac.
Another thing I've wondered about is whether my using numbers of minutes not contained in the regular suggested numbers is a problem. For example, I often use 20 minutes instead of the suggested 15 minutes. iCal accepts it and it usually works, but once in a while, it changes to 15 hours. I verify and re-verify that I'm entering the correct numbers. I've been doing that since I noticed the problem.
Does iCal use Java? Apple has been killing Java & requiring re installation to a later version of Java a couple of times lately. I know I'm grasping at straws, but I'm sick of the problem.
