Ubuntu Desktop - Customize Unity Time & Date Indicator

Enable the clock indicator:

gsettings set com.canonical.indicator.datetime show-clock true

Set the indicator to use the custom format:

gsettings set com.canonical.indicator.datetime time-format custom

Set the actual format to use:

gsettings set com.canonical.indicator.datetime custom-time-format "%A, %B %e  %l:%M %P"

NOTE: The different options that can be used in the format string can be found on the strftime function man page.

References