This tip applies mostly to task lists, but also applies to document libraries.
It is standard for SharePoint Online to present dates in a friendly format, such as Sunday, or February 15, Yesterday or Tomorrow.
Some people prefer to just see the dates themselves and don’t like seeing the friendly dates.
Here’s how you go about changing that.
Go to click on the LIST tab and click on list settings (in a library you would go to the library tab and then library settings.)
Scroll to about the middle of the page to where the list of columns are, and click on the date field you want to change.
About midway down the settings screen you will see Display Format.
Change this setting as you need to, to set it to Standard or Friendly format.
Then choose SAVE