Just one more solution:
$('a').on('click', function(e){
var $link = $(e.target);
e.preventDefault();
if(!$link.data('lockedAt') || +new Date() - $link.data('lockedAt') > 300) {
doSomething();
}
$link.data('lockedAt', +new Date());
});
Here we save the time of last click as data attribute and then check if previous click was more than 0.3 seconds ago. If it is false (less than 0.3 sec ago), just update last click time, if true, do something.