Get the Time WordPress Post was Published

I was creating a WordPress plugin and needed to get the time (specifically the year) posts were written or published.
Thanks to get_post_time function, i was able to get the time posts were published.

Here is a my plugin function that returns the year posts were published.

< ?php

function displayNotification($content) {
	global $post;

	//get post year eg 2014
	$post_year = get_post_time('Y', true, $post -> ID);

	return $content;
}

UPDATE: am sorry for not explaining what the role of $content in the code.
I added it because i need the code above to get post years as the plugin i built needed to check the year of post against the current year to see if the post is older than a given number of years and then display some sort of message above post content.
Thus, the a filter needed to be hooked to the_content filter to achieve the purpose.

Below is the filter hook.

add_filter('the_content', 'displayNotification');

Take note, the first argument of get_post_time is PHP time and date character therefore, you can not only retrieve the post year, but also the month, date or mixed time & date format as specified by the date/time format character.

Just hope someone find this useful.