The date settings may display with the month before the day (mm/dd/yy) in Office 365. To resolve this issue, please follow the steps below.
The time zone and locale settings are not set to 'UTC Dublin,Edinburgh, London' in your Office 365 account.
1.Go to the Staff iD page and select the Mail link in the top left of the screen;
2.Log in with your firstname.lastname@example.org account, then click the settings (cog) icon;
3. Select Site settings;
4. Select the Regional Settings link under Site Administration;
5. Set the Locale to 'English (United Kingdom)' and ensure the Time Zone is set to UTC Dublin,Edinburgh, London.