Try this:
- portal.azure.com
- click on Settings (gear close to your account name)
- pick "Language + region"
The date and time format will be dependent on your locale settings--it will either be from your operating system level or browser. Such as you are using Chrome, you can change the default display language of Google Chrome.
More detail about this issue, please refer to this ticket: https://developercommunity.visualstudio.com/content/problem/428156/azure-devops-project-where-can-i-set-the-date-form.html