What you did wrong here is the part ```date('d', $rem_days)```.

When you use something like that, if you have the number of days more than one month, the function ```date()``` with ignore that and only count the number of days. So for example, when the duration is **1 month and 14 days**, it will instead show **14 days**. 

You can fix this by replacing ```date('d', $rem_days)``` with ```floor($remaining_time/86400)```. 

The complete code should be:
```
$event_date = strtotime( get_field( 'event_date', false, false ) );
$curr_date  = time();
$rem_days   = $event_date - $curr_date;
if ( $rem_days <= 0 ) {
	$event_msg = '<strong>Event Expired</strong>';
} else {
	$event_msg = '<strong>' . floor( $rem_days / 86400 ) . '</strong> Days Remaining';
}
```