How to get time difference between publish date and now?

I want to get time difference like “posted 2 days ago”.

I know you can use the following to get the difference.

human_time_diff( get_the_time('U'), current_time( 'timestamp' ) ) . ' ago';

But I don’t want to use that

        date_default_timezone_set('Australia/Melbourne'); // set the time zone
        $timestamp = strtotime( $post->post_date ); // get timestamp
        $now =  time();// get the curren time
        $time_passed = $timestamp - $now; // get the differnece

    // display time
    $min = $time_passed / 60;
    if( $min < 60 ) {
        return sprintf( avantgardia__( '%s min. ago', 'newspeak' ), intval( $min) );
    }

Try the date_diff() / DateTime::diff() function in PHP:

// Object-oriented style.
$datetime1 = new DateTime( $post->post_date );
$datetime2 = new DateTime(); // current date
$interval = $datetime1->diff( $datetime2 );
echo $interval->format( '%a days old' );

// .. or procedural style.
$datetime1 = date_create( $post->post_date );
$datetime2 = date_create(); // current date
$interval = date_diff( $datetime1, $datetime2 );
echo $interval->format( '%a days old' );

In PHP 5.2.2 or later, you can compare the date (“ago” vs “later”) like so:

if ( $datetime1 < $datetime2 ) {
    echo $interval->format( 'Published %a days ago.' );
} elseif ( $datetime1 > $datetime2 ) {
    echo $interval->format( 'Will be published in %a days later.' );
} else {
    echo 'Published today.';
}