I think I know you from the bbc films website. I certainly don't believe that cinema is entirely "immune" to time. Of course, our frame of reference for discussing this only goes back to the beginning of the 20th Century (the beginning of film). It's not the same as looking back to ancient Greece! But maybe it's not all that different.
I suppose there are certain standards of beauty, drama, and other aspects of art that will always be common to the human race. But art is still very much subject to time. Most people today would be more moved watching a dramatic play about contemporary life and issues than a play by Aeschylus, for example. In the realm of cinema, a lot of contemporary viewers are completely unmoved and disinterested when they watch a film from the 1940's or 50's, for example.
On the other hand, I could give a counter example from my own experience in the form of, say, 'Maedchen in Uniform.' I think the film is aesthetically beautiful; the fact that it was made in 1931 means nothing to me, perhaps other than the idea that it was from an era of cinematic greatness long past. Yet, someone 500 years from now may look at that film and react to it the way that I react to Chaucer's "Canterbury Tales" -- with a very indifferent shrug. Chaucer could have been the voice of his generation in his time, but I look at the "CT" as something basically absurd and alien.