I have a US English installation of Outlook 2013 on Windows 8. I customized the regional settings to display date as d/M/yy and time as HH:mm on my system.

When I am in calendar visualization and I move my mouse on an appointment a pop-up tip comes out giving me the details of the appointment. But in that pop-up the date format is WRONG. On all other visualization in Outlook 2013 the time seems to comply with the regional settings. The only exception is that pop-up. Notice that the time format is, on the other hand, correct.

See picture: the meeting is meant to take place on 2-July-2013 and it should appear as 2/7/2013 not 7/2/2013. 

How can I force that date format to comply with the regional settings?

Than

Hi,

You are right. The only explanation could be Outlook uses a specified date format for the calendar tip and the feature might not be changed. In the situation, I would suggest to create support case with Microsoft:

http://support.microsoft.com/oas

Best regards,