I agree that his current study habits are the sign of someone who is not managing his time well but not currently suffering from it in his mind, meaning his grades are still good. He is unfortunately, however, learning bad study habits which will not put him in good stead for the more challenging courses and time pressures of high school.
All we can do as parents, with kids of this age, is to calmly offer our opinions and assistance and then step back and let our children do "their job". If they do ask for our help after their poor decisions get them in trouble, we must not scold them for not heeding our advice, we must simply praise them for seeking out solutions to their difficulties. Your son will learn and grow based on what he demands from himself as well as your continued unconditional support.