There are a few answers to this that help with the gnome taskbar date-time display, and one answer that gives me exactly what I want, namely,
date +%Y-%m-%dT%T
which I've incorporated into .bashrc as an alias. Now, is there a way to change date permanently? Or do you always have to add these options? I'm afraid some programming I will do might not access a bash alias or I'll forget to add the options.