Custom Date in Top Bar in Ubuntu

The Clock Override GNOME Shell Extension can be used to change the format of the date displayed in the top bar.

The GLib Reference Manual contains the format specifiers that can be used to build the date format.

I have used the following format:

%A, %e %B %Y - %l:%M %p

The displayed string is:

Sunday, 16 June 2019 - 8:25 PM