Exercise

How exercise affects your sleep

Immediately after: increased energy and alertness
Later that day: fall asleep more quickly and sleep longer

Exercise promotes sleep in several ways

Increases body temperature which then falls afterwards. Falling body temperature triggers falling asleep and staying in a deep, slow wave sleep.
Modules circadian rhythm: helps you feel alert or sleepy when you need to be
Alleviates stress and anxiety that would otherwise disrupt sleep

Q: When is the best time to exercise to promote sleep?
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A: One large study found that exercise improved sleep less if it was performed in the evening versus afternoon, but another large study found the timing of exercise on average did not affect sleep

It is possible that exercise timing matters relative to your circadian rhythm. Some studies have suggested that exercise can shift your internal body clock (Process C) forward or backward, meaning the time you feel sleepy will be affected by the time you exercise.
BUT, it is difficult to determine this for sure, since the time of day people exercise affects many other factors like the timing of light exposure and eating.
Bottom line: the time of day you exercise could affect your sleep, but you need to experiment and figure out the best time that works for you.
Most importantly, remember that exercise helps promote sleep.

Sources:

1. The Effects of Acute Exercise on Sleep: A Quantitative Synthesis, Sleep.

2. 2013 Sleep in America Poll, National Sleep Foundation.