WordPress pretty timestamp function. 'Posted 1 day ago' / 'Posted 2 hours ago' etc.

functions.php

/**
 * Echoes a pretty timestamp if the post is younger than max_days.
 * Must be used inside the loop.
 *
 * Examples:
 *     - Posted 3 days ago
 *     - Posted 12 hours ago
 *     - Posted 5 minutes ago
 *     - Posted just now (less than a minute ago)
 *     - 2014-07-25 08:33:54 (post is older than $max_days)
 * 
 * @param  integer $max_days The maximum age of the post before reverting to
 *                           traditional timestamps.
 */
function the_pretty_timestamp( $max_days = 7 ) {
    $post = get_post();
    
    $one_day = 60 * 60 * 24;
    $one_hour = 60 * 60;
    $one_minute = 60;

    $post_age = current_time( 'timestamp' ) - strtotime( $post->post_date );

    if ( ! is_numeric( $post_age ) || ( $post_age / $one_day ) > $max_days ) {
        echo $post->post_date;
        return;
    }

    $days = round( $post_age / $one_day );
    $hours = round( $post_age / $one_hour );
    $minutes = round( $post_age / $one_minute );

    if ( $days >= 1 ) {
        echo 'Posted ' . $days . ' day' . ( $days > 1 ? 's' : '' ) . ' ago';
    } else if ( $hours >= 1 ) {
        echo 'Posted ' . $hours . ' hour' . ( $hours > 1 ? 's' : '' ) . ' ago';
    } else if ( $minutes >= 1 ) {
        echo 'Posted ' . $minutes . ' minute' . ( $minutes > 1 ? 's' : '' ) . ' ago';
    } else {
        echo 'Posted just now';
    }
}