Can you try replacing this hot mess with:

```php
    public function settingsImportInterval()
    {

echo <<<HTML
       <span>
         <input class="small-text" type="number" min="{self::MIN_IMPORT_INTERVAL}" step="1" name="{self::IMPORT_INTERVAL_OPTION}" value="{get_option(self::IMPORT_INTERVAL_OPTION)}">
       </span> Minimum {self::MIN_IMPORT_INTERVAL} seconds.
HTML;

This is string building is specific to PHP. It's called "heredoc" http://www.php.net/manual/en/language.types.string.php#language.types.string.syntax.heredoc

    }
```