As an update, since we’ve still been seeing issues around date formatting, so we’re pursuing another fix that should help: If you’re using Planner within Teams, we will default to using the same language/local as Teams.
If you’re seeing this issue persist outside of Teams and your language/locale is set properly for your Office account, please let us know in the comments below!
The Planner Team
An error occurred while saving the commentDave Rawstorne commented
Using Version 1.3.00.21759 of Teams (an August 2020 release) I changed my Language in Teams->Settings to English (New Zealand) and then chose 'Save and Restart'. Dates in Planner are now correct for New Zealand.
Remember to 'Save and Restart' for it to take effect!