In WordPress esiste questa funzione che permette di calcolare il tempo trascorso tra due date.
Generalmente serve per indicare le date in una maniera diversa. Nei commenti o nei post.
Ad esempio: “Questo post è stato pubblicato 3 mesi fa.”
La funzione che viene utilizzata è human_time_diff che si trova in /wp-includes/formatting.php .
Purtroppo la funzione porta le indicazioni  in inglese

function human_time_diff( $from, $to = '' ) {
if ( empty( $to ) )
$to = time();

$diff = (int) abs( $to - $from );

if ( $diff < HOUR_IN_SECONDS ) {
$mins = round( $diff / MINUTE_IN_SECONDS );
if ( $mins <= 1 )
$mins = 1;
/* translators: min=minute */
$since = sprintf( _n( '%s min', '%s mins', $mins ), $mins );
} elseif ( $diff < DAY_IN_SECONDS && $diff >= HOUR_IN_SECONDS ) {
$hours = round( $diff / HOUR_IN_SECONDS );
if ( $hours <= 1 )
$hours = 1;
$since = sprintf( _n( '%s hour', '%s hours', $hours ), $hours );
} elseif ( $diff < WEEK_IN_SECONDS && $diff >= DAY_IN_SECONDS ) {
$days = round( $diff / DAY_IN_SECONDS );
if ( $days <= 1 )
$days = 1;
$since = sprintf( _n( '%s day', '%s days', $days ), $days );
} elseif ( $diff < 30 * DAY_IN_SECONDS && $diff >= WEEK_IN_SECONDS ) {
$weeks = round( $diff / WEEK_IN_SECONDS );
if ( $weeks <= 1 )
$weeks = 1;
$since = sprintf( _n( '%s week', '%s weeks', $weeks ), $weeks );
} elseif ( $diff < YEAR_IN_SECONDS && $diff >= 30 * DAY_IN_SECONDS ) {
$months = round( $diff / ( 30 * DAY_IN_SECONDS ) );
if ( $months <= 1 )
$months = 1;
$since = sprintf( _n( '%s month', '%s months', $months ), $months );
} elseif ( $diff >= YEAR_IN_SECONDS ) {
$years = round( $diff / YEAR_IN_SECONDS );
if ( $years <= 1 )
$years = 1;
$since = sprintf( _n( '%s year', '%s years', $years ), $years );
}

return $since;
}

per tradurla, possiamo ricopiarla nel file functions.php e rinominarla ad esempio human_time_diff _ita

function human_time_diff_ita( $from, $to = '' ) {
if ( empty( $to ) )
$to = time();

$diff = (int) abs( $to - $from );

if ( $diff < HOUR_IN_SECONDS ) {
$mins = round( $diff / MINUTE_IN_SECONDS );
if ( $mins <= 1 )
$mins = 1;
/* translators: min=minute */
$since = sprintf( _n( '%s minuto', '%s minuti', $mins ), $mins );
} elseif ( $diff < DAY_IN_SECONDS && $diff >= HOUR_IN_SECONDS ) {
$hours = round( $diff / HOUR_IN_SECONDS );
if ( $hours <= 1 )
$hours = 1;
$since = sprintf( _n( '%s ora', '%s ore', $hours ), $hours );
} elseif ( $diff < WEEK_IN_SECONDS && $diff >= DAY_IN_SECONDS ) {
$days = round( $diff / DAY_IN_SECONDS );
if ( $days <= 1 )
$days = 1;
$since = sprintf( _n( '%s giorno', '%s giorni', $days ), $days );
} elseif ( $diff < 30 * DAY_IN_SECONDS && $diff >= WEEK_IN_SECONDS ) {
$weeks = round( $diff / WEEK_IN_SECONDS );
if ( $weeks <= 1 )
$weeks = 1;
$since = sprintf( _n( '%s settimana', '%s settimane', $weeks ), $weeks );
} elseif ( $diff < YEAR_IN_SECONDS && $diff >= 30 * DAY_IN_SECONDS ) {
$months = round( $diff / ( 30 * DAY_IN_SECONDS ) );
if ( $months <= 1 )
$months = 1;
$since = sprintf( _n( '%s mese', '%s mesi', $months ), $months );
} elseif ( $diff >= YEAR_IN_SECONDS ) {
$years = round( $diff / YEAR_IN_SECONDS );
if ( $years <= 1 )
$years = 1;
$since = sprintf( _n( '%s anno', '%s anni', $years ), $years );
}

return $since;
}

e usarla dove la funzione deve mostrare parole in italiano