Hey bexx! It's not true that you'll burn "at the same rate" for 24 hours. It depends what type of exercise you've done, but you will burn SOME calories, just not 600 per hour. After low-moderate 'cardio' (aerobic exercise) your body returns fairly quickly to resting levels, usually within about an hour after exercise. ACSM reports that you may burn 20-30 calories extra during that post-cardio hour. There are many studies out there suggesting that after strength training, you will burn more calories for a much longer period, 24 - 36 hours in some cases. This depends on the intensity of the strength training session and the actual number of calories that you burn per hour hasn't really been agreed upon yet.
The amount of calories burned post-exercise is not really enough to worry about. You will not burn nearly as many calories during recovery from exercise as through regular exercise sessions!
Hope that helps!