Outlook2010 reminder pop-up appears, set at 5 minutes before the event.
I click the postpone option to reset to 4 hours, but it still keeps popping up every 5 minutes instead of only after 4 hours.
What's going on there?

Try to start outlook with the switch /cleansniff . Then try /cleanreminders to clear and reset all reminders
path to outlook\outlook.exe /cleansniff.
I hope it would help you.

It also might have happened due to Corrupt Calendar Entry, if it is the case then follow the given Steps :
1. Open Outlook Calendar. Then, select Calendar from the Outlook top navigation bar.
2. From the top navigation Go to View Current View and select All Appointments
3. Select the recurring and then, click the delete button to remove the appointment from Outlook.
4. Close the Outlook and then restart it to check if the problem still exists or not.

If the problem still continues, there might be some other issue such as a hard drive failure etc.

How do I do that?