This appears to be a built-in way to achieve that (v1.7.4):
git for-each-ref --sort=committerdate refs/heads/ --format='%(committerdate:short) %(refname:short)'
I've enjoyed the @Will Sheppard solution to put some colors.
git for-each-ref --sort=committerdate refs/heads/ --format='%(color: red)%(committerdate:short) %(color: cyan)%(refname:short)'