Settings API in Section

Here you go my friend:

add_filter( 'admin_init' , 'register_fields' );

function register_fields() 
{
    register_setting( 'general', 'msp_duration', 'esc_attr' );
    add_settings_field( 'msp_duration', __('Cache Duration') ,'fields_html', 'general' );
}

function fields_html() 
{
    $value = get_option( 'msp_duration' );
    $fields = array(
        array(
            "name"  => __('Every 6 hours'),
            "value" => 60 * 60 * 6,
        ),
        array(
            "name"  => __('Every 12 hours'),
            "value" => 60 * 60 * 12,
        ),
        array(
            "name"  => __('Every 24 hours'),
            "value" => 60 * 60 * 24,
        ),
        array(
            "name"  => __('Every 48 hours'),
            "value" => 60 * 60 * 48,
        ),
        array(
            "name"  => __('Every Week'),
            "value" => 60 * 60 * 24 * 7,
        ),
    );

    $output="<select name="msp_duration">";

        foreach( $fields as $option ) 
        {
            $output .= '<option value="'. $option['value'] .'" '. selected( $option['value'], $value, false ) .'>';
                $output .= $option["name"];
            $output .= '</option>';
        }

    $output .= '</select>';

    echo $output;
}

Use the value with: get_option( 'msp_duration' );