IIRC, the qualitative (or proven quantitative) connection between exercise and improved sleep is most pronounced with morning exercise (HIIT/weight lifting).
This is interesting to me, do you know any articles about this? I feel when I put off exercise until later in the evening(after 7pm) that I often get poorer quality sleep, but I'd be surprised if working out at 6am vs. lunchtime would make that much a difference.
I used to have to work out late at night (like 8-10pm), and found that 30+ mins of low intensity cardio and a long period of relaxed stretching after the workout helped.
