file1.php

class Custom_Submission_Limit extends GW_Submission_Limit {

	public function is_applicable_form( $form ) {
		$form_id = isset( $form['id'] ) ? $form['id'] : $form;
		return in_array( $form_id, array( 2, 3, 4, 5, 9 ) );
	} 

}

# Configuration

# Basic Usage
new Custom_Submission_Limit( array(
	'limit_by' => 'field_value',
    'limit' => array(
        // "18" is your field ID, "1" is your limit for this field ID
        18 => 1 
    ),
    'time_period' => 60 * 60 * 24 * 10,
    'limit_message' => 'Ati trimis deja o solicitare in ultimele 10 zile.'
) );