Don't burn yourself out, but what you're doing actually isn't that uncommon. Well, for marathon runners, anyway.
The body only starts to burn fat after 30 minutes of exercise, normally, because it will first go through the phosphagen energy system and the glycolysis energy system (burns carbs) before it switches to the oxidative energy systems (burns fats, and to a lesser extent, proteins). So longer workouts would technically mean more fat burned in this way.
HOWEVER! A long workout like that will also burn muscle protein. I know you say "not worrying about muscle loss" but I wonder why this is. More muscle = more fat loss. The amount of muscle you have often determines the amount of energy your body tries to utilize in the form of fat. Since larger muscles require more energy to support them, they will burn more calories throughout the day and result in more fat loss.