There are a couple of unwritten conventions being used for this in our codebase, one is what this code uses, the other is:

```php
wfWhatever( $par1, $par2, 86400 /* 24 hours */ );
```

I find the second one to be more descriptive, someone that stumbles upon a function call for the first time with 60*60*24 being passd in, might not infer it's a time unit right away.