You can customize the way the date and time are shown by selecting the "Date Format" tab in your Blog page's "Setup..." area.

Blog - Setup: Date Format Tab

On this pane, you can specify how the date and time are displayed, including separators. As you make changes to the settings, an example is displayed in the lower portion of the pane. To localize the language to that of the one being used by your Macintosh, click the "Localize language" checkbox.