The default Nucleus blog layout groups items written on one specific day under a date header (in English):
21 August
The date format and language are controlled by your templates (default/index and default/item on a default install). You can change these under the
Date and Timetemplate section, which you will find after some scrolling down on a template page.
The exact date format, which you specify in the
Date Headerfield under
Date and Time, utilizes the PHP date function. The date quoted above is the result of the following code entered into the
Date Headerfield:
%d %B
You can change that to your liking.