Override the Gnome Shell clock with a new time format or text of your choice. Works with new versions of Shell such as 3.18.
If you're looking to use this extension, don't get it from here; this is for developers. To add this extension to your desktop, click here to get it from extensions.gnome.org.
Gnome Shell doesn't permit many changes to the format of its clock; in particular, it's not possible to remove it completely or to add text around it. That's what this extension is for: you can set the clock's "format string" to change how the Gnome Shell clock is displayed (do you want it as HH:MM? HH.MM? "10:37:21 am"?), including setting it to just a fixed string (for example, a bell) so you have somewhere to click to see notifications and calendar but no clock on-screen.
For techies, we use the GLib GDateTime codes to specify actual times in your clock string, with two additions:
%f, a little Unicode clock character (thanks to dsboger for that!%@, internet time (.beat)
Note that we still try to honour Gnome Shell's clock settings. So if you expect your clock to show seconds (or to update once a second, rather than once a minute) then you'll need to have turned on "show seconds" in Gnome Tweak Tool (under Top Bar) (or the terminal way).