Set it to three minutes- like a round of boxing- with a one minute rest. Hit it for three minutes; do three rounds. 130 is a bit heavy, for my way of thinking, as that would mean less swing; that makes you keep your feet moving, teaches you how to work with and around a body in close. When you work on the heavy bag, don't just throw punches, but decide before hand which punch or combination you are going to focus on each day/round/ whatever and go about setting it up, working the bag for position etc.. Also, don't hit it then either stand there, drop your hands, or back straight out. This is called bad habit development; work your way in and jab out, or something but practice doing it right all the time.