If I haven't eaten, 45 minutes since your body doesn't start burning calories until after 15 minutes of working out. This is where the notion that working out in the morning is best - With no food to process first, the body burns fat faster.
If I have eaten then I'm on the treadmill for 1 hr 15 minutes.
If I have eaten then I'm on the treadmill for 1 hr 15 minutes.