The artist’s work, that is related to the passage of time in the natural world, but does not depict a specific subject, is an example of Non-representational art.
What is non-representational art?
Non-representational art is an art form that does not depict any recognizable objects or scenes from the real world. Instead of these, it uses shapes, colors, lines, and forms to create a composition that is independent of external references.
Also, this type of art is considered more expressive and personal than representational art, because it allows the artist to convey their emotions and ideas in a more direct and unfiltered way.