I have a user with this problem: Notes sends calendar reminders at the wrong time. Additionally, the date/time stamp on emails is wrong, sometimes by 15 minutes, sometimes more. For example, at 12:48 pm, his incoming emails showed a time stamp of 1:30 pm and he got an alert for a 2 pm meeting (should have been 30 minutes before). The user has experienced this problem in all versions of 6.5x. His PC is set to have “perfect Internet time”, yet Notes does not reflect this. The problem is inconsistent; it happens for a while, then goes away for a while.
Subject: Notes doesn’t show correct time
You checked that the Notes client is using the OS time settings? Some people will tinker and override those things.
Also, in my experience, a problem with the timestamp on messages tends to come from a time issue on the mail server. May wish to double-check that.