What makes something timeless? Why do some bands from the eighties still sound awesome while others sound like an electronic experiment gone wrong?
Or, how about fashion? Why do colors come and go, while black always remains cool? White ponytails are nowhere to be seen, yet we still listen to Mozart. Why?
How do we create timeless art? The difference is in the audience. Mozart wrote beautiful music, but it came from within. It wasn't because he wanted to copy what was popular. He created what became popular. The difference can be seen in a painter who paints to please his audience versus painting to please himself.
There is no rule book for making timeless art. There are "suggestion books", but ultimately the art has to come from you. A timeless song speaks not to the ears, but to the soul. There are probably millions of portraits of women, but there is only one Mona Lisa.
This is the beauty of "timeless". It is the magic of something so profound that there really is no explanation--only wonder through the ages. This is the essence of timeless art, and the only one who can make it, is you.