Can I use strtotime() to obtain the timestamp for a given day 'last month' and if not what is the most efficient way of doing this?

This is the kind of thing I want

```
strtotime("5 last Month");

```

instead of 

```
$time_day= 5;
$time_month= date("m");
$time_year= date("Y");

if($time_month<1){
$time_month=12;
$time_year--;
}else{
$time_month--;
}

$date=mktime(0,0,0,$time_month,$time_day,$time_year);

```