I'm guessing on this one based on experience, and things I heard over the years.
Physical activity releases chemicals, which make you calmer and (most likely) happier after the workout. Also, exercising takes up your glucose supply. Glucose gives you energy and it's stored in your body. This is why marathon runners often build up on carbs (where glucose is found) the day/week before the marathon. Anyways, the shortage of glucose makes you hungry. Lack of glucose= lack of energy. Lack of energy means you're tired, which makes you want to sleep. BUT. The period between finishing the workout and feeling the need to sleep are different for everyone.
Exercising increases blood flow through the body and brain, improving everything overall, including time management. Your body is better able to tell when to be awake and when to be asleep.
Hope that helped! :)
*DISCLAIMER*: ALWAYS CHECK WITH A RELIABLE SOURCE!
This information may NOT be accurate, so PLEASE check with a reliable source! I'm not responsible if you get an incorrect answer. Please verify with someone or something! :)
Thanks for reading, and have a wonderful day! :)
