Gravity Forms once per day

<?php
add_filter('gform_validation_1', 'custom_validation');
function custom_validation($validation_result){
    global $wpdb;
    $email_field = 6;
    $form = $validation_result["form"];
    $error_message = "You can only submit a vote once every calendar day. Please come back later!";
    foreach($form["fields"] as &$field) {
        if ( $field['id'] == $email_field ) {
            $email_value = rgpost("input_{$field['id']}");
            $entry_submission = $wpdb->get_var( $wpdb->prepare(
                "SELECT lead_id FROM {$wpdb->prefix}rg_lead_detail
                WHERE form_id = %d and field_number = %d and value = %s
                ORDER BY id DESC LIMIT 1", $form['id'], $field['id'], $email_value ));

            if ( !empty( $entry_submission ) ) {
                $last_submission = $wpdb->get_var( $wpdb->prepare(
                    "SELECT date_created
                    FROM {$wpdb->prefix}rg_lead
                    WHERE id = %d", $entry_submission ));

                if ( !empty( $last_submission ) ) {
                    $time_out = date("Ymd", strtotime($last_submission) );
                    $current_time   = date("Ymd");

                    if ( $current_time == $time_out ) {
                        $validation_result['is_valid'] = false;
                        $field["failed_validation"] = true;
                        $field["validation_message"] = $error_message;
                        continue;
                    }
                }
            }
        }
    }

    $validation_result["form"] = $form;
    return $validation_result;
}