Mac outlook reminders always late Just reiterating a few locked threads that I found reporting the same issue but without any solution/conclusion:

Calendar reminders - noticeable delay
Calendar reminders in Outlook for Mac v15.3 show up late
Calendar Reminders late on desktop
Calendar/Reminder Notifications Late

And hopefully some day somebody can have an answer.
For my case, MBP desktop,

reminders for first pop up (say 15 mins) and then when snoozed to (say) 5 mins before are normally on time (when pop up shows, the time on the URH corner is still the same, say 9:45, 9:55)
however, it is the the final reminder at the time of the event that constantly show up late, range from 50 seconds to 1.5 minutes (when pop up shows, the time on the URH corner is almost always at least a minute late, say 10:01+)
and today, the final reminder show up one hour late

My OS: Mac Catalina
$ sw_vers                
ProductName:       Mac OS X
ProductVersion: 10.15.7
BuildVersion:   19H524
I think I have an answer, I'm not sure yet, but let me throw it out first, so people can verify....
Today, after my reminder was late for almost 5 minutes, I have a theory --
The final reminder should be triggered on time, but what I suspect is that its triggering time is 5 minutes after you last click on the &quot;Snooze&quot; button.