Late Night Cardio

I had a simple day planned today. I did some homework in the morning and then worked in the evening. I didn't have the chance to work out before work so I got it done at 10pm. All I had to do was some cardio so it didn't take too long. I did 5 minutes on the stair master to warm up. I did 10 intervals on the treadmill: 1 minute walk, 30 second jog, and a 30 second sprint. It wasn't too difficult and it was over before I knew it. I really feel that my cardio is improving. My heart rate doesn't go up as quickly as it used to. I'm feeling great and ready for bed. I have to be up and back at the gym for 9!