How to pull a message from queue with time interval?

edit

When I subscribe my node, I set messages queue size and callback function:

int main(int argc, char **argv) {

    ros::init(argc, argv, "scs_drive");

    ros::NodeHandle n;

    ros::Subscriber sub = n.subscribe("scs", 1000, writePosCallback);

    ros::spin();
    return 0;
}

The incoming messages are being processed as soon as previous callback function operations are finished. But I want to process incoming messages from queue not ASAP but each millisecond.

So maybe it is possible to pull messages here:

int main(int argc, char **argv) {

    ros::init(argc, argv, "scs_drive");

    ros::NodeHandle n;

    ros::Subscriber sub = n.subscribe("scs", 1000, writePosCallback);

    ros::Rate loop_rate(1000);

    while (ros::ok()) {

        //some code here that pulls message from queue and process incoming data

        ros::spinOnce();
        loop_rate.sleep();
    }

    return 0;
}

Or I need to set pause in callback function and it is the one choice to process messages with a certain time interval?