Since your apparent height changes from the morning to the evening, you can't have a permanent condition like spondylolisthesis.
In the morning, people are taller because the discs the spine are able to rehydrate and fill with fluid while no compression is being applied to them. During the day, due to our upright posture, gravity and other compressive forces squeeze some of the fluid back out of the discs. This makes us shorter at the end of the day. This also makes the spine more flexible. Think of a hose filled with water versus a flaccid hose; which bends more easily?
This might account for the change in mobility you get from morning to evening. If it isn't affecting you in any other way (no pain, no loss of function), then I would stop worrying about it so much. Extreme sidebending in the frontal plane is an unnatural motion anyway and feels awkward for most people.